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Lattice-matched Al1−xInxN / GaN heterostructures with InN mole fraction (x) of 0.18 have attracted considerable interest for use in GaN-based optoelectronic devices. Because the light emission efficiency (η emission ) of Al1−xInxN alloys is far less than that of InxGa1−xN, understanding its causes is essential. For this purpose, room-temperature photoluminescence lifetime (τ PL RT ), which almost represents the nonradiative recombination lifetime that limits the internal quantum efficiency in low η emission semiconductors, of c-plane Al1−xInxN epilayers nearly and modestly lattice-matched to GaN (0.11 ≤ x ≤ 0.21) was examined. For the epilayers grown on low threading dislocation density (TDD) GaN substrates (≪ 10 7 c m − 2 ), τ PL RT principally decreased with increasing x, indicating a progressive increase in the concentration of nonradiative recombination centers (NRCs), N NRC . One of the probable causes is the growth temperature (T g ) reduction that is indispensable to incorporate more In, because in insufficient T g regime higher T g is preferred for enhancing the surface migration of adatoms to decrease the concentrations of vacancies that compose NRCs. The Al1−xInxN epilayers of the same x but grown on high TDD (> --> 10 8 c m − 2 ) GaN-on-sapphire templates exhibited shorter τ PL RT . Because the diffusion length of minority carriers was nearly zero in the Al1−xInxN epilayers, the shorter τ PL RT indicates higher bulk N NRC in high TDD epilayers. The Al1−xInxN epilayers of considerably rough surface morphologies exhibited spatially inhomogeneous τ PL RT , implying that excited carriers recombined everywhere at InN-rich to InN-poor portions, where N NRC were likely lower to higher, respectively, than the average due to the deviations in the surface stoichiometry at various non-c-plane surfaces at a given T g . [ABSTRACT FROM AUTHOR]

A record-long room-temperature photoluminescence (PL) lifetime ( τ PL RT ) of approximately 70 ps was obtained for the sub-bandgap 3.7 eV emission band of a 300-nm-thick c-plane Al0.83In0.17N epilayer for the use in cladding layers of an edge laser structure, which were grown by metalorganic vapor phase epitaxy on a low threading dislocation density nearly lattice-matched GaN substrate. The recorded τ PL RT value was twice as long as previously reported ones, indicating half concentration of nonradiative recombination centers. Room-temperature spatially resolved cathodoluminescence intensity images for the 3.7 eV band revealed nearly zero carrier diffusion length, which is consistent with the fact that τ PL RT of 70 ps is 1/35 of the near-band-edge emission of the GaN substrate (2.4 ns). As the PL decay curves for the 3.7 eV band were sufficiently fitted by the stretched exponential function, the emission likely originates from extended states such as impurities, point defects, and their complexes, as well as localized states of uneven potential profile. [ABSTRACT FROM AUTHOR]

The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN. [ABSTRACT FROM AUTHOR]

The authors report on the effect of metal-precursor gas ratios on AlInN/GaN structures for high efficiency ultraviolet photodiodes. AlInN/GaN structures with the different metal-precursor gas ratio, namely V/III ratio, were grown on AlN templates by metal organic chemical vapor deposition. Nearly lattice-matched AlInN layer is obtained at the higher temperature by decreasing the V/III ratio. AlInN layers are found to have good crystal qualities with no dependency on the V/III ratio. However, pit density depends slightly on the V/III ratio, indicating good surface morphology is obtained by decreasing the V/III ratio. The fabricated photodiodes also show good device characteristics by decreasing the V/III ratio. The spectral responsivity at the cutoff wavelength increases from 1 to 20 mA/W, indicating that the quantum efficiency is greatly improved. We believe that the further optimization of the growth parameters for AlInN/GaN structures is one of the effective approaches in realizing high efficiency ultraviolet photodiodes. [ABSTRACT FROM AUTHOR]

The mechanism of the effect of n-GaN thickness on the internal quantum efficiency (IQE) in InxGa1-xN multiple-quantum-wells (MQWs) grown on GaN/Si by means of metal organic chemical vapor deposition has been investigated by x-ray diffractometry, photoluminescence, and transmission electron microscopy. It is found that the increasing n-GaN thickness obviously improves the IQE in InxGa1-xN MQWs. It is clarified that the threading dislocation density (TDD) directly determines the V-defect density and the V-defect density is lower than the TDD. As the n-GaN thickness increases from 1.0 to 2.0 μm, the TDD significantly decreases by one order of magnitude. The V-defect density obviously reduces from 3.9 × 109 cm-2 to 8.7 × 108 cm-2, while the IQE in InxGa1-xN MQWs is improved from 28.3 to 44.6%. As the GaN thickness increases, the V-defect density in the InxGa1-xN MQW decreases due to the reduction of TDD in GaN, and subsequently the nonradiative recombination centers are effectively eliminated due to the reduction of the V-defect density in the InxGa1-xN MQWs. [ABSTRACT FROM AUTHOR]

GaN-based light-emitting diodes (LEDs) grown on template of 3C-SiC/Si(111) were demonstrated. The structural properties have been investigated systematically by means of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. It is found that the intermediate layer (IL) of 3C-SiC leads to not only a significant improvement in the crystalline quality of GaN, but also better interfaces between the buffer layer and the initial layers of strained-layer superlattice. The device properties were also evaluated using the measurements of current-voltage, electroluminescence, and light output power-current. Compared to conventional LEDs that do not contain 3C-SiC IL, the device with IL exhibits enhanced output power by more than 200% at an injection current of 20 mA, and the operating voltage is slightly increased from 3.7 to 3.9 V. These results indicate that using 3C-SiC as IL is one of the promising approaches to improve the performance of LEDs on silicon. [ABSTRACT FROM AUTHOR]

Pd Schottky barrier diodes were fabricated on undoped AlxIn0.02Ga0.98-xN/GaN with x less than 20%. The material properties, which were characterized by photoluminescence, x-ray diffraction, and atomic force microscopy, indicated that the quaternary samples were coherently grown on GaN template with high crystalline quality. The flatband barrier height obtained by capacitance-voltage (C-V) measurement increased with increasing Al mole fraction (increasing the band gap of the quaternary) up to 2.06 eV, in agreement with the predictions of the Schottky-Mott theory. However, current-voltage (I-V) measurements revealed that the barrier height decreased from 1.32 to 1.12 eV, which was accompanied by an increase in ideality factor from 1.04 to 1.73. The large difference of barrier height between I-V and C-V measurements could not be quantitatively explained by the traditional electron transport mechanisms of Schottky diode, such as tunneling effect, image force effect, and barrier inhomogeneity theory. Strong polarization effect in strained AlxIn0.02Ga0.98-xN/GaN heterostructure was proposed to account for the experimental results, since similar phenomena had been observed extensively in strained AlyGa1-yN/GaN heterojunction structures. [ABSTRACT FROM AUTHOR]

The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (E[sub FX]) of AlGaN alloys in Al[sub x]Ga[sub 1-x]N/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in Al[sub x]Ga[sub 1-x]N/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the E[sub FX]s obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the E[sub FX], the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (x≤0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0≤x<0.3, the resulting bowing parameter shows a downward value of 0.53 eV. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode. Metalorganic chemical vapor deposition on a sapphire substrate; Electrical and optical degradations under high injected current density and high ambient temperature; Observations of electroluminescence, electron-beam induced current and cathodoluminescence.

Deals with a study of the crystallinity of gallium arsenide grown on silicon with various intermediate layers by metalorganic chemical vapor deposition and characteristics of Schottky diodes fabricated on the grown gallium arsenide/silicon. Experimental details; Results and discussion; Conclusion.

We report the characteristics of InGaN multiple-quantum-well (MQW) green light-emitting diodes (LEDs) on Si (111) substrates. The MQW LEDs were grown on Si by metalorganic chemical vapor deposition using Al[sub 0.27]Ga[sub 0.73]N/AlN intermediate layers. The LED on Si showed an operating voltage of 7 V, a series resistance of 100 Ω, an optical output power of 20 μW, and a peak emission wavelength of 505 nm with a full width at half maximum of 33 nm at 20 mA drive current. The optical output power was half as compared to that of green LED on sapphire. The LED also exhibited a stable operation over 500 h under automatic current control (20 mA) condition at 27 °C. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study that examined the interfacial roughness and compositional profile of the AlAs/GaAs distributed Bragg reflectors structure by cross-sectional scanning electron microscopy, transmission electron microscopy and Auger electron microscopy. Methodology of the study; Results and discussion on the study; Conclusion.

The authors report on Al2O3/Al0.85In0.15N/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) on Si fabricated by using atomic layer deposited Al2O3 as gate insulator and passivation layer. The MOS-HEMT with the gate length of 2 µm exhibits excellent direct-current (dc) characteristics with a drain current maximum of 1270 mA/mm at a gate bias of 3 V and an off-state breakdown voltage of 180 V for a gate-drain spacing of 4 µm. Also, the 1 µm-gate MOS-HEMT shows good radio-frequency (rf) response such as current gain and maximum oscillation cut-off frequencies of 10 and 34 GHz, respectively. The capacitance-voltage characteristics at 1 MHz revealed significant increase in two-dimensional electron gas (2DEG) density for the MOS-HEMT compared to conventional Schottky barrier HEMTs. Analyses using drain-source conductivity measurements showed improvements in 2DEG transport characteristics for the MOS-HEMT. The enhancements in dc and rf performances of the Al2O3/Al0.85In0.15N/GaN MOS-HEMT are attributed to the improvements in 2DEG characteristics. [ABSTRACT FROM AUTHOR]

The InxAl1-xN/GaN system is found to show compositional instability at the lattice-matched composition (x = 0.18) in epitaxial layers grown by metal organic chemical vapor deposition. The breakdown in compositional homogeneity is triggered by threading dislocations with a screw component propagating from the GaN underlayer, which tend to open up into V-grooves at a certain thickness of the InxAl1-xN layer. The V-grooves coalesce at ∼200 nm and are filled with material that exhibits a significant drop in indium content and a broad luminescence peak. Transmission electron microscopy suggests that the structural breakdown is due to heterogeneous nucleation and growth at the facets of the V-grooves. [ABSTRACT FROM AUTHOR]

The authors report the effect of sulfide treatment on electrical characteristic of Pd/InAlN Schottky diode. Quantitative analysis considering different current-transport mechanisms revealed that the sulfide treatment not only significantly reduced leakage current but also almost completely suppressed a tunneling current between InAlN surface and Pd contact, which could be attributed to the surface passivation of InAlN with forming S-N and S-O bonds as revealed by x-ray photoelectron spectroscopy (XPS) measurements. As a result of the treatment, the reverse-biased current was reduced significantly by more than one order of magnitude at -5 V to be as low as 3.95 × 10-8 A/cm2, and by more than two orders of magnitude at -10 V to be 1.27 × 10-7 A/cm2, corresponding to the record-low values reported to date. [ABSTRACT FROM AUTHOR]

Low-temperature AlN grown on AlGaN/GaN heterostructure in situ by metal-organic chemical vapor deposition is used as gate insulator and passivation layer to form quasi-normally-off field-effect transistors on 4 in. silicon substrate. The AlN layer not only increases the sheet carrier density and mobility, which results in the increase of the maximum drain current and transconductance, but also decreases gate leakage and current collapse. Simulated band diagrams indicate that only a small potential difference exists between the AlN surface barrier height and the AlN/AlGaN interface. We show that low-temperature grown AlN is effective in suppressing trapping effects and in improving device performance. [ABSTRACT FROM AUTHOR]

Temperature-dependent photoluminescence (PL) measurements have been performed on high-quality InAlN layers lattice-matched (LM) to GaN with different thicknesses. It is found that the PL is consisted of two components denoted as IH (high-energy side) and IL (low-energy side), respectively. IH is attributed to exciton luminescence of bulk InAlN with linewidth comparable to those calculated under the assumption of perfect random alloy. While IL is attributed to the emission from the quantum-dotlike structure on the surface of InAlN, revealing the importance of surface effect to the investigations related to InAlN LM to GaN. [ABSTRACT FROM AUTHOR]

The temperature-dependent electroluminescence (EL) properties of AlGaN deep ultraviolet light-emitting diodes (LEDs) have been studied. The low-temperature EL quenching is observed in 265 nm LEDs with p-type AlGaN heterostructure, which has not previously been reported in such short wavelength devices. However, this phenomenon disappears in those with a thin i-AlN electron blocking layer (EBL). It is found that the electron overflow becomes more severe at low temperature in the LEDs without EBL, whereas it is suppressed effectively in those with AlN EBL. On the basis of a model of temperature-dependent efficiency, the EL quenching is explained by the competition of electron overflow and radiative recombination. [ABSTRACT FROM AUTHOR]

A series of InxAl1-xN-based Schottky solar-blind photodiodes are fabricated on the InxAl1-xN epilayers with high and very close crystal qualities. The quantum efficiency varies from 14.5% to 68.5%. The microstructure and strain state of epilayers are investigated in detail. It is found that the quantum efficiency of photodiode depends on the strain state in InxAl1-xN films. This indicates that adjusting the strain state in InxAl1-xN film is one of the promising approaches to optimize the performance of InAlN-based solar-blind photodiode. [ABSTRACT FROM AUTHOR]

The authors report the growth of InxAl1-xN with high crystal quality by metal organic chemical vapor deposition, the Pd/InxAl1-xN Schottky contacts with reverse current densities as low as 6.0×10-7 A/cm2 at -5 V and 2.1×10-5 A/cm2 at -10 V, and consequently significant improvement in the performance of InAlN-based Schottky solar-blind photodiodes with peak responsivity of 133 mA/W at 242 nm, corresponding to a quantum efficiency of 68.5%. The illumination is detectable under the intensity as weak as 10 nW/cm2. The rejection ratios by 300 nm are one order of magnitude for 10 nW/cm2 illumination and three orders of magnitude for 1 μW/cm2 illumination. [ABSTRACT FROM AUTHOR]

The origin and suppression of the subband parasitic peak in AlGaN deep ultraviolet light-emitting diodes have been studied. The parasitic peak is clarified to come from a p-AlGaN cladding layer and to be related to Mg dopants. By using 1 nm i-AlN as an interlayer between the active region and the p-AlGaN cladding layer, this peak is suppressed efficiently. The devices with such an interlayer show improved output power by a factor of 4 at injection current density of 20 A/cm2, except that the series resistance and turn-on voltage are slightly increased. [ABSTRACT FROM AUTHOR]

AlInN, one of the III-nitride semiconductors, is expected to find its application as transistors, sensors, light emitters of electronic, and optoelectronic devices. When the lattice alignment of AlInN is made similar to GaN, a great deal of crack-free AlInN film growth is possible on GaN layers. We have successfully grown AlInN and AlGaN films by metal organic chemical vapor deposition. The structural analysis for the metal organic chemical vapor deposition grown films show that they have the same structure and were used to produce AlInN and AlGaN-based ultraviolet (UV) photodiodes. This paper describes the growth and fabrication of AlGaN and AlInN-based UV photodiodes and analyzes their device performance. For an AlInN, the peak responsivity at zero bias was measured to be 140 mA/W at 230 nm, corresponding to an external quantum efficiency of 74%. AlInN was found to be more suitable than AlGaN for UV photodiodes with a cutoff wavelength in the UV-C range. [ABSTRACT FROM AUTHOR]

The behavior of electroluminescence (EL) and junction temperature of AlInGaN deep ultraviolet light-emitting diodes under pulse-width modulation is investigated. The redshift of both emissions from quantum-well (P1) and localized (P2) states in the EL spectra and the increase of intensity ratio of P1 to P2 are observed with the increase of duty cycle. The photoluminescence of p-GaN contact layer is adopted to measure the junction temperature, which shows a linear relation with the duty cycle. Meanwhile, the duty cycle coefficient of junction temperature increases with the increase of injection current. The EL behaviors are explained by the thermal effect induced by pulse current at high duty cycle. [ABSTRACT FROM AUTHOR]

The correlation between the crystalline quality of low-temperature GaN (LT-GaN) films and current collapse in AlGaN/GaN heterostructure field-effect transistors with a LT-GaN cap layer was investigated. LT-GaN cap layers were grown at various temperatures ranging from 450 to 700 °C. No current collapse was observed for heterostructure field-effect transistors with LT-GaN cap layers grown at 500 and 550 °C. The crystalline quality of the 1-μm-thick LT-GaN films grown at 450–700 °C was then studied through x-ray diffraction and selected area electron diffraction measurements. The crystalline quality, considered by measuring the full width at half maximum through x-ray diffraction, deteriorated as the growth temperature decreased. The crystal structure of LT-GaN films grown at 500 and 550 °C was confirmed as polycrystalline. Thus, the results demonstrated that in AlGaN/GaN heterostructure field-effect transistors, a polycrystalline structure provides the most effective LT-GaN cap layer for suppressing current collapse. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN heterostructures (HSs) with high two dimensional electron gas mobility (1070 cm2/V s) were grown on nonpolar a-plane (1120) sapphire substrate by metal organic chemical vapor deposition. High crystalline quality (reduced screw, edge, and mixed dislocations) with small root mean square surface roughness and small peak-valley distance values were observed in a-plane sapphire grown AlGaN/GaN HSs. Hexagonal-GaN phase was also observed on a-plane sapphire grown AlGaN/GaN HSs. An average increase of ns up to 22% for a plane and 26% for c plane were found after Si3N4 passivation. The product of ns and μH also increases for both a-plane (19%) and c-plane (28%) sapphire grown AlGaN/GaN HSs in a wide range of measurement temperature (87–400 K). The enhancement of sheet carrier density by Si3N4 passivation for nonpolar (1120) sapphire grown AlGaN/GaN HSs is a useful result for the design of future GaN high-electron-mobility transistors. [ABSTRACT FROM AUTHOR]

Injection current and temperature dependence of electroluminescence (EL) is investigated in AlInGaN deep untraviolet light-emitting diodes. Two EL bands with different behaviors are observed. The high-energy band (P1) shows a monotonous redshift and an amazing increase of intensity with increasing current, however, a “U”-shaped shift and a saturation of intensity at high current are measured for the low-energy band (P2). Accordingly, P1 and P2 are attributed to emissions from quantum-well and localized states, respectively, with P1 dominant at high current and high temperature and P2 the main emission mechanism under low temperature and low current. Modeled data based on the theory of random population for localized states in quantum wells taking into account self-heating effect agree well with the experimental results. [ABSTRACT FROM AUTHOR]

The authors report the high-performance AlGaN solar-blind Schottky photodiodes grown on AIN/sapphire templates by metal organic chemical vapor deposition. The devices exhibit dark current densities as low as 1.6×10-11 A/cm2 at -5 V bias. The peak responsivity is 41 mA/W at 256 nm in the photovoltaic mode, corresponding to a quantum efficiency of 20%. A sharp spectral response cutoff of more than two orders of magnitude by 300 nm is observed under a low illumination intensity of 10 nW/cm2. The zero-bias resistance-area product of the device is found to be 5.0×1012 Ω cm2, leading to an estimated detectivity of 7.0×1014 cm Hz1/2/W at 256 nm. [ABSTRACT FROM AUTHOR]

Light emitting diodes (LEDs) on GaN templates with high-density V-shaped micropits have been grown and characterized by transmission electron microscopy, scanning electron microscopy, and photoluminescence. Higher emission efficiency has been obtained for the fabricated LEDs compared with those without V-shaped pits. The high efficiency of the LEDs is mainly attributed to the increase in light extraction efficiency due to the light extraction from the sidewalls of the V-shaped pits. The improved internal quantum efficiency of the device resulting from the reduction of the dislocation density in the light emitting area also contributes to the high efficiency of the LEDs. [ABSTRACT FROM AUTHOR]

Crack-free AlGaN layers were grown on AlN/sapphire templates by low-pressure metalorganic chemical vapor deposition. Reduction of threading-dislocation (TD) density is achieved by inserting a high-temperature GaN interlayer between the AlGaN and AlN layers. Structural characterization reveals that such an interlayer can efficiently block the TDs propagating from the underlying AlN layer, and reduce the TD density in the subsequent AlGaN layer by one order of magnitude with an optimum thickness of 25 nm. It is also clarified that the decrease of edge TDs is the dominant contribution to this reduction. [ABSTRACT FROM AUTHOR]

Undoped AlInGaN/GaN heterostructure field-effect transistors (HFETs) have been demonstrated on sapphire substrate. The maximum drain current of 758 mA/mm and extrinsic transconductance of 123 mS/mm were obtained from the device with 2 μm gate length and 15 μm gate width. Such performance was comparable to that of a conventional modulation-doped (MOD) AlGaN/GaN HFET fabricated at same the condition. In spite of the high-density two-dimentional electron gas formed at the heterointerface, the AlInGaN/GaN HFET structure showed relatively low Hall mobility (689 cm2/V s at 300 K), which was due to the high concentration background doping in the undoped AlInGaN barrier region. Encouragingly, both the gate leakage current and drain current collapse showed lower values than that of the MOD-AlGaN/GaN HFET, which implied the potential application of quaternary AlInGaN to high-power and high-frequency devices. [ABSTRACT FROM AUTHOR]

Enhancement of breakdown voltage (BV) with the increase of AlN buffer layer thickness was observed in AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by metalorganic chemical vapor deposition on 4 in. Si. The enhancement of device performance with AlN buffer thickness (200 and 300 nm) is due to the reduction of electrically active defects from Si substrate. The reduction of defects from Si with the increase of AlN thickness was confirmed by x-ray rocking curve measurements. Not much change has been observed in ON-state BV (BV:ON) values except in devices with 500-nm-thick buffer layer. About 46% enhancement in OFF-state BV (BV:OFF) was observed on 200 μm wide HEMTs with 300 nm thick AlN buffer layer when compared to HEMTs with 8 nm thick AlN buffer layer. The location of junction breakdown in the device was identified as GaN/AlN/Si interface. The measured specific on-resistance (Ron) values for 200 and 400 μm wide HEMTs with 300 nm thick buffer layers were 0.28 and 0.33 mΩ cm2, respectively. About an order of low Ron was observed when compared with the reported values. The AlGaN/GaN HEMTs on 4 in. Si with thicker AlN buffer layers are suitable for high-power applications. [ABSTRACT FROM AUTHOR]

Pd/Ti/Au and Ni/Au Schottky barrier diodes (SBDs) were demonstrated on quaternary AlInGaN. Current–voltage properties indicated that near-ideal and high-performance SBDs had been realized with ideality factor of 1.05, 1.07 and barrier height of 1.32, 0.98 eV for Pd and Ni SBDs, respectively. Capacitance–voltage measurement revealed that the high-density two-dimensional electron gas (2DEG) located at the AlInGaN/GaN interface. Ruling out the possible contribution from piezoelectric polarization and conduction band offset, we believe that the formation of 2DEG is due to the existence of large spontaneous polarization in AlInGaN layer, which experimentally verifies the feasible application of quaternary AlInGaN in the high-electron-mobility transistor. [ABSTRACT FROM AUTHOR]

Drain current (ID) collapse-free i-GaN/AlGaN/GaN high-electron-mobility transistors (HEMTs) with and without surface passivation (electron-beam evaporated SiO2) were demonstrated using dc and pulsed (120 Hz) IDS–VDS characteristics up to the drain supply voltage of 40 V. The observation of small ID transients and negligibly small hysteresis widths with small white light illumination effects on both passivated and unpassivated i-GaN/AlGaN/GaN HEMTs confirms the suppression of collapse related traps. Three and two thermally activated trap levels were observed in passivated (+0.395, -0.079, and -0.949 eV) and unpassivated (-0.066 and -0.368 eV)AlGaN/GaN HEMTs, respectively. However, i-GaN/AlGaN/GaN HEMTs with and without surface passivation exhibited only one trap level at -0.161 eV. These results show that the addition of thin cap layer i-GaN screens the collapse-related surface states/traps from channel. [ABSTRACT FROM AUTHOR]

Al0.26Ga0.74N/AlN/GaN heterostructures with 1-nm-thick AlN interfacial layers were grown on 100-mm-diam epitaxial AlN/sapphire templates and sapphire substrates by metalorganic vapor phase epitaxy. It was found that AlN/sapphire templates significantly enhanced the electron mobility of the two-dimensional electron gas (2DEG) confined at the GaN channel. This can be explained by the high-crystal-quality GaN channel realized by the use of epitaxial AlN/sapphire templates as substrates. The very high Hall mobilities of approximately 2100 cm2/V s at room temperature and approximately 17 000 cm2/V s at 77 K with a 2DEG density of approximately 1×1013/cm2 were uniformly obtained for AlGaN/AlN/GaN heterostructures on 100-mm-diam epitaxial AlN/sapphire templates. The Hall mobility of AlGaN/AlN/GaN heterostructures on epitaxial AlN/sapphire templates reached a very high value of 25 500 cm2/V s at 15 K. [ABSTRACT FROM AUTHOR]

An efficient method has been investigated to grow GaN films with sapphire substrates being treated in situ metalorganic chemical vapor deposition reactor for a special effect rather than simple thermal cleaning. First, a thin GaN layer is grown on the sapphire substrate. And then it is almost etched away by thermal decomposition. It is found that the decomposition of GaN induces the decomposition of sapphire resulting in the formation of high-density nanocraters on its surface. Finally the device-quality GaN film is regrown on the etched substrate with residual gallium droplets as nucleation sites. The chemistry of the etching process and the mechanism of the final GaN growth process have been discussed. The distinct feature of this method is the in situ formation of high-density nanocraters on the surface of the substrate. A rough interface between the substrate and GaN can improve the efficiency of the light-emitting diode built on it greatly. [ABSTRACT FROM AUTHOR]

Surface passivation effects were studied on AlGaN/GaN high-electron-mobility transistors (HEMTs) using SiO[sub 2], Si[sub 3]N[sub 4], and silicon oxynitride (SiON) formed by plasma enhanced chemical vapor deposition. An increase of I[sub Dmax] and g[sub mmax] has been observed on the passivated (SiO[sub 2], Si[sub 3]N[sub 4] and SiON) HEMTs when compared with the unpassivated HEMTs. About an order of magnitude low I[sub gLeak] and three orders of magnitude high I[sub gLeak] was observed on Si[sub 3]N[sub 4] and SiO[sub 2] passivated HEMTs, respectively, when compared with the unpassivated HEMTs. The increase of I[sub gLeak] is due to the occurrence of surface related traps, which was confirmed by the observation of kink and hysteresis effect on dc and ac I[sub DS]–V[sub DS] characteristics, respectively. Though the Si[sub 3]N[sub 4] passivated HEMTs show better dc characteristics, the breakdown voltage (BV[sub gd]) characteristics are not comparable with SiO[sub 2], SiON passivated and unpassivated HEMTs. The SiON is also a very promising candidate as a surface passivant for AlGaN/GaN HEMTs because it shows better BV[sub gd] with low hysteresis width and small I[sub D] collapse than Si[sub 3]N[sub 4] passivated HEMTs. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A series of InGaN/GaN multiple quantum wells (MQWs) was grown by metalorganic chemical vapor deposition with different well thickness. High-resolution x-ray diffraction studies revealed that the In composition is increasing along the growth direction from the bottom to the top of each well layer in these MQWs. While the In composition at the bottom of each well layer almost keeps constant, the increasing rate of In composition becomes obviously larger when the growth temperature is decreased. The important conclusion of this study is that the InGaN/GaN MQWs is shaped like a triangle due to the increasing of In composition from the bottom to the top of the well layer. The emission mechanism of the InGaN/GaN MQWs has to be discussed based on the triangular band gap structure. [ABSTRACT FROM AUTHOR]

We report on the studies of the temperature dependence of gate-leakage current in AlGaN/GaN high-electron-mobility transistors (HEMTs) for the temperature range 20-400 °C. The results show that the temperature dependence of gate-leakage current for AlGaN/GaN HEMTs at subthreshold regime (V[sub GS] = -6.5 V) have both negative and positive trends. It has been observed that the leakage current decreases with the temperature up to 80 °C. Above 80 °C, the leakage current increases with the temperature. The negative temperature dependence of leakage current with the activation energy +0.61 eV is due to the impact ionization. The positive temperature dependence of leakage current with the activation energy -0.20 eV is due to the surface related traps, and the activation energy -0.99 eV is due to the temperature assisted tunneling mechanism. The drain voltage at a fixed drain-leakage current reveals the occurrence of both positive (+0.28 V/K) and negative (-0.53 V/K) temperature coefficients. [ABSTRACT FROM AUTHOR]

The drain-current collapse at high drain voltage has been studied in AlGaN/GaN high-electron-mobility transistors (HEMTs) on both semi-insulating (SI)-SiC and sapphire substrates using small frequency (120 Hz) sinusoidal wave superimposed dc I[sub DS] - V[sub DS] characteristics. Low drain-current collapses were observed in AlGaN/GaN HEMTs on SI-SiC substrate when compared with the HEMTs on sapphire substrates. Two and three thermally activated deep traps were observed on SiC-based and sapphire-based HEMTs, respectively. The existence of an additional deep trap (ΔE = 0.61 eV) could be associated with the material defects/dislocations responsible for the severe drain current collapse in sapphire-based HEMTs. The white-light illuminated I[sub DS] - V[sub DS] characteristics support the existence of more number of deep traps in the sapphire-based HEMTs. [ABSTRACT FROM AUTHOR]

High-electron-mobility transistors (HEMTs) have been demonstrated on both AlN/sapphire templates and sapphire substrates, and the dc characteristics of the fabricated devices were examined at room temperature. Better dc characteristics with high extrinsic transconductances and drain current densities were observed in the HEMTs grown on AlN/sapphire templates when compared with the HEMTs on sapphire substrates. Extrinsic transconductances of 214 and 137 mS/mm for W[sub g]/L[sub g]= 15/2 µm HEMTs on AlN/sapphire templates and HEMTs on sapphire substrates were achieved, respectively. The enhancement of dc characteristics with small variations in threshold voltage (≤ 130 mV) is due to the reduction of dislocation density (1.5 × 10[sup 8] cm[sup -2]). The decrease of dark spot density has been confirmed in the GaN grown on AlN/sapphire templates using cathodoluminescence measurements. The advantage of using AlN/sapphire templates is that low dislocation density GaN layers at a high temperature can be grown without using low-temperature-grown GaN buffer layers. [ABSTRACT FROM AUTHOR]

Structural, electrical, and optical properties of an InGaN-based light-emitting diode (LED) on an A1N/sapphire template have been studied and compared with the conventional LED properties on a sapphire substrate. In comparison to the LED on sapphire, the LED on A1N/sapphire template has shown better electrical and optical characteristics, which are due to a low threading dislocation density, high resistive, and thermal conductive A1N layer. An additional advantage is to grow a high-quality LED structure on an A1N/sapphire template without using low-temperature-grown GaN or an A1N buffer layer. [ABSTRACT FROM AUTHOR]

The high-electron-mobility transistors (HEMTs) have been demonstrated on both sapphire and semi-insulating (SI) SiC substrates, and the dc characteristics of the fabricated devices were examined at temperatures ranging from 25 to 500 °C. The decrease in drain current and the transconductance with the increase of temperature have been observed. The decrease ratio of transconductance and drain current was similar for both the HEMTs on sapphire and SI-SiC substrates at and above 300 °C. The HEMTs on SiC substrates showed better dc characteristics after being subjected to thermal stress up to 500 °C. Although the SiC-based HEMTs showed better characteristics up to the temperature of 300 °C, compared with the sapphire-based HEMTs, similar dc characteristics were observed on both at and above 300 °C. For high-temperature applications (≥300 °C), additional cooling arrangements are essential for both devices. [ABSTRACT FROM AUTHOR]

GaN films were grown on sapphire and SiC substrates. The crystal qualities of GaN films were investigated by photoluminescence, atomic force microscopy, and electron-beam-induced current measurements, etc. It was found that the crystal quality of GaN on SiC is better than the one on sapphire. Ni/Au Schottky contacts were formed on the both samples. The electronic characteristics were obtained by current–voltage and capacitance–voltage measurements. Schottky diodes on sapphire substrate show breakdown voltage of -80 V. While for SiC substrate, the strong breakdown was not observed even at -100 V. The reverse leakage current of diodes based on SiC is over three orders of magnitude lower than that of sapphire substrate when the reverse voltage is above 50 V, which is due to the presence of low dislocation density and high thermal conductivity. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the characteristics of GaAs metal-semiconductor field-effect transistors on silicon substrates. Back-coating of the substrates with silicon dioxide metalorganic chemical vapor deposition; Improvement of crystallinity of GaAs layers grown on silicon.

We demonstrate the first room-temperature low-threshold continuous-wave (cw) operation of Al0.3Ga0.7As/GaAs single quantum well (SQW) heterostructure lasers grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates using techniques of SiO2 back coating and thermal cycle annealing. The all-MOCVD-grown SQW lasers on GaAs/Si with etch pit density of 1.5× 107 cm-2 have threshold current as low as 55 mA (1.41 kA/cm2) under cw at room temperature. The SiO2 back coating is effective to obtain excellent current-voltage characteristics. Thermal cycle annealing is also found to improve the crystallinity of GaAs/Si and to contribute to room-temperature cw operation of the lasers on Si substrates. [ABSTRACT FROM AUTHOR]

We report an optical degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) on a sapphire substrate grown by metalorgonic chemical vapor deposition. Electroluminescence, electron-beam induced current, and cathodoluminescence observations have shown that the degraded InGaN/AlGaN LED exhibits formation and propagation of dark spots and a crescent-shaped dark patch, which act as nonradiative recombination centers. The values of degradation rate under injected current density of 0.1 kA/cm2 were determined to be 1.1×10-3, 1.9×10-3, and 3.9×10-3h-1 at ambient temperatures of 30, 50, and 80°C, respectively. The activation energy of degradation was also determined to be 0.23 eV. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the growth of self-formed gallium arsenide (GaAs) islands on GaAs/silicon substrate by metalorganic chemical vapor deposition. Use of atomic force microscope; Function of trimethylgallium flow rate; Fabrication of aluminum GaAs/GaAs light-emitting diode on silicon.

Develops an Al-free reliable 877 nanometer In[sub0.49]Ga[sub0.51]P/GaAs light emitting diodes (LED) on Si substrates by metalorganic chemical vapor deposition. Effects of dark line defects (DLD) on the conventional Al-containing Al[sub0.3]Ga[sub0.7]As/GaAs LED on silicon substrates; Factor suppressing DLD formation.

Examines the degradation of the AlGaAs/GaAs well laser diodes on silicon substrates grown by metalorganic chemical vapor deposition. Cause of increase in threshold current and decrease in differential quantum efficiency; Effect of the defect-assisted impurity diffusion; Reason for the rapid occurrence in degradation process.