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Comments on J.K. Lao and colleagues' article 'Piezoelectric Effect on AlInGaN/GaN Heterostructures.' Effect of a small fraction of In atoms in AlInGaN/GaN on the piezoelectric field at the interface; Schematic illustration of the band structure in the triangular potential quantum well; Origin of the beating oscillations; Zero-magnetic-field spin splitting.

Al and GaN contacts on both Si(111) and sapphire substrates were studied in this letter. After annealing at 450, 520, 600, and 650 °C for 35 min under a N[sub 2] flowing ambient, the current-voltage characteristics of Al/GaN contacts on Si(111) substrates were different from those on sapphire ones. The interfacial properties were discussed using the Schottky emission model in which the current is proportional to the square of the applied voltage. The metallurgical reactions were analyzed using photoluminescence (PL) spectra and x-ray diffraction (XRD). After annealing, blueshifts in the PL spectra and new peaks in the XRD data indicated that the wide-band gap interfacial phase AlGaN was formed at the Al/GaN interface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A metal-ferroelectric-semiconductor (MFS) structure has been developed by depositing SrBi[sub 2]Ta[sub 2]O[sub 9] (SBT) films directly on n-type (100) Si by pulsed laser deposition. In the MFS structure, evidence for ferroelectric border traps in the SBT film has been obtained by high-frequency capacitance-voltage (C-V) measurement. When the ramp rate of voltage is higher than 200 mV/s, typical ferroelectric C-V hysteresis loops with the counterclockwise direction are obtained in C-V plots. When the ramp rate is lower than 80 mV/s, the ferroelectric hysteresis loops are replaced by the trap-induced ones with the clockwise direction. This pronounced change results from the fact that more and more border traps in SBT can communicate with the underlying Si. The border-trap density at the ramp rate of 10 mV/s is as high as 1.8x10[sup 12] cm[sup -2]. Moreover, the width of the hysteresis loops changes linearly with the logarithmic decrease in ramp rate, which is consistent with the ferroelectric border traps communicating with Si by tunneling or a thermally activated process. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

GaN metal-semiconductor-metal photoconductive detectors have been fabricated on Si(111) substrates. The GaN epitaxial layers were grown on Si substrates by means of metalorganic chemical-vapor deposition. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at a wavelength from 360 to 250 nm. A maximum responsivity of 6.9 A/W was achieved at 357 nm with a 5 V bias. The relationship between the responsivity and the bias voltage was measured. The responsivity saturated when the bias voltage reached 5 V. The response time of 4.8 ms was determined by the measurements of photocurrent versus modulation frequency. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The characteristics of low-frequency noise in n-metal-oxide-semiconductor field-effect transistors with ultranarrow channels have been investigated through random telegraph signals and low-frequency noise spectroscopy. Random telegraph signals with very large amplitude (∼70%) are observed in weak inversion at room temperature. Low-frequency noise spectra having both 1/f[sup n] and Lorentzian type are found separately in the same channel at various gate bias voltages. The observations strongly suggest that the low-frequency noise is dominated by carrier mobility fluctuation in weak inversion and by carrier number fluctuation under high-field conditions in an ultranarrow channel. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The effect of alloying and expitaxial mismatch strain on the surface ultraviolet (UV) emission efficiencies of AlxGa1−xN films, pseudomorphically grown on both c- and m-plane AlyGa1−yN templates (x−0.03+1.79x−0.06x2 (0

Abstract: Impact of anisotropic strains on low-frequency dielectric properties and room-temperature polar phases of SrTiO3 epitaxial thin films is investigated. The dielectric properties show a remarkable change as a function of anisotropic strains. The number of room-temperature polar phases is as twice as that of isotropically strained SrTiO3 thin films. [Copyright &y& Elsevier]

Abstract: We have grown Fe3N films on GaN(0002) substrates by metalorganic chemical vapor deposition (MOCVD). Under lower growth temperatures, small iron particles were formed on GaN surface, while under higher growth temperatures, Fe3N films were formed. The surface morphology of samples with different growth temperatures were characterized by atomic force microscopy. In X-ray Photoelectron Spectroscopy (XPS) measurement, the coexistence of metallic Fe and Fe2+ or Fe3+ was observed in the sample grown at 600°C, while the sample grown at 1050°C showed only high valence forms of Fe ions. It was also found that the magnetic moments of Fe3N prefer to align normal to the c-axis. [Copyright &y& Elsevier]

Abstract: The alloy Al x Ga1− x N was grown by metal-organic chemical vapor deposition (MOCVD) using a high-temperature AlN interlayer on a thick GaN template. The Al composition (x) of the Al x Ga1− x N was varied in the range 0.13⩽x⩽0.8. The in-situ reflectance spectra indicate that the growth process of AlGaN alloys is dominated by trimethylgallium (TMGa) molar flux when the molar flux of trimethylaluminium (TMAl) is kept constant. The Al compositions and growth rates of AlGaN alloys were determined by Rutherford backscattering, which indicates that the incorporation efficiency of TMAl is improved remarkably by decreasing the TMGa molar flux. The crystalline quality of these AlGaN alloys is evaluated by measuring the symmetric (002) and asymmetric (102) ω-scan X-ray diffraction peak widths. The best crystalline quality, among these Al x Ga1− x N alloys, is for an Al composition of x=0.54 where the full-width at half-maximums of the AlGaN (002) and (102) diffraction peaks are 265 and 797arcsec, respectively. This conclusion is consistent with the surface morphology of the AlGaN alloys probed by atomic force microscopy. Room temperature cathodoluminescence spectra show pronounced near band edge emission from these AlGaN alloys. The optical band gaps (E g) are found to deviate from linear interpolation between E g GaN and E g AlN with a bowing parameter b=0.89. [Copyright &y& Elsevier]

Abstract: In this paper, hydrogenated amorphous silicon nitride (a-SiN x :H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH3 flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH4 +NH3 plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si3N4 was also convinced in Si-rich SiN x films by XPS. Either photo- or electroluminescence for all the SiN x films with R >3 sccm shows a strong light emission in visible light wavelength range. As R <6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN x films, however, for photoluminescence, gap states'' luminescence is also in competition; as R >6 sccm, light emission of the SiN x film originates from defect states in its band gap. [Copyright &y& Elsevier]

Abstract: The circular photogalvanic effect (CPGE) is observed in InN at inter-band excitation. The function of the CPGE induced current on laser helicity is experimentally demonstrated and illustrated with the microscopic model. A spin-dependent current obtained in InN is one order larger than in the AlGaN/GaN heterostructures at inter-band excitation. The dependence of CPGE current amplitude on light power and incident angle can be well evaluated with phenomenological theory. This sizeable spin-dependent current not only provides an opportunity to realize spin polarized current at room temperature, but also can be utilized as a reliable tool of spin splitting investigation in semiconductors. [Copyright &y& Elsevier]

Abstract: The fluid dynamics of a vertical metal-organic chemical vapor deposition (MOCVD) reactor for the growth of ZnO film have been studied. The relevant transport equations were solved by numerical integration using a finite volume difference method. Computation results show that the deposition rate strongly depends on the operating parameters of the MOCVD reactor. Simulation results show that the reactor pressure has effect on the deposition rate, which becomes larger with the increment of the reactor pressure in the range of low pressure in our study. The simulated deposition rate is observed to increase firstly and then decrease with the main carrier gas flow rate. The computational study demonstrates that the distance between the O2 inlet and substrate in the vertical MOCVD reactor plays a key role to obtain a balance between the deposition rate and the uniformity of films across the substrate. The optimization of the MOCVD operational parameters has been applied in the MOCVD growth of high-quality ZnO epilayers. [Copyright &y& Elsevier]

Abstract: High reflectivity (>93.5%) distributed Bragg reflectors (DBRs) have been successfully produced using the AlGaN/AlN multilayer stacks materials system by metal-organic chemical vapor deposition (MOCVD). The peak reflectance of the DBRs was located at 320nm. The nominal Al composition is 30%, and the layer thicknesses of the different periods stack were designed for a target wavelength of 330nm. We present reflectivity, SEM, AFM and XRD data of Al x Ga1− x N/AlN Bragg reflectors grown on (0001)-oriented sapphire. The surface of the AlN/AlGaN DBRs was found to grow in quasi-two-dimensional (2D) mode, which was indicated by the atomic force microscopy (AFM). The DBR has very smooth surface and the interface was distinct. [Copyright &y& Elsevier]

Abstract: This paper reports the high mobility InN film grown by MOCVD with GaN buffer layer on sapphire substrates. Different buffer layers are used in our experiments. These buffer layers included the annealing sapphire substrate, the low-temperature GaN layer (LT-GaN), the high-temperature GaN layer (HT-GaN) and the complex buffer layer with HT-GaN on LT-GaN. The crystalline quality of the InN film is sensitive to the underlying buffer layer when the film is grown under the high effect V/III ratio condition. And the growth conditions are optimized in our system. We employed the three-step buffer layer with HT-GaN and LT-GaN on annealing sapphire. The mirror like layers on 2in sapphire wafers was obtained. The structure, optical and electrical characteristics of InN was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence (PL) and IR optical absorption. The PL and the absorption studies of the materials reveal a marked energy band gaps structure around 0.70eV, at room temperature. The uniformity of morphology and the electrical property of the grown InN film are markedly improved by using the complex buffer layer with HT-GaN and LT-GaN on the annealing sapphire. The InN film grown by this buffer layer has the carrier concentration of 3.9×1018 cm−3 and the Hall mobility of 939cm2/Vs. [Copyright &y& Elsevier]

Abstract: AlN/Al0.3Ga0.7N distributed Bragg reflectors (DBRs) are grown on sapphire (0001) by metal-organic chemical vapor deposition (MOCVD). The number of stacks of the DBRs varies between 6 and 30. The thickness of the quarter-wave layers is designed such that the target peak reflectance locating at the wavelength of 330nm. The GaN or AlGaN templates are employed for growing the AlN/AlGaN DBRs. It is found that the templates intensively influence on the surface roughness and the interfacial properties of AlN/AlGaN DBRs. The result of atomic force microscopy indicates that the AlN/AlGaN DBRs grow on GaN template under quasi-two-dimensional mode. And the good interfaces of AlN/AlGaN not only clearly observed by cross-sectional scanning electron microscopy, but also concluded from narrow width and high orders of satellite peaks detected by high-resolution X-ray diffraction. The peak reflectance of 20 stacks DBRs on GaN template reaches up to 82% located at 326nm.While those DBRs grown on AlGaN template do not show such structural and optical properties due to the rough surface of AlGaN template and the poor interfaces of AlN/AlGaN. [Copyright &y& Elsevier]

Abstract: We have grown single crystalline GaMnN films by a horizontal hydride vapor-phase epitaxy (HVPE) system. The structures and crystal quality were confirmed by XRD and Raman scattering measurements. The structure analysis indicated that we obtained uniform GaMnN solid-solution films; the Mn atoms were substituted for Ga sites and did not form Mn precipitates or clusters. The superconductor quantum interference device (SQUID) results show that the GaMnN films without the phase separation exhibit paramagnetic properties. [Copyright &y& Elsevier]

Abstract: Zn1− x Ni x O (, 0.02 and 0.05) powders were prepared by a sol–gel method. We have studied the structure and magnetic properties of the samples by using X-ray diffraction (XRD), Raman scattering, superconducting quantum interference device (SQUID) and extended X-ray absorption fine structure (EXAFS). The SQUID results showed that all the samples exhibit ferromagnetism above room temperature. From the XRD spectra of the samples, it was obvious that there had no second phase while the Ni-doped concentration was lower than 5at%. Raman spectra showed an additional band, which is related to the vibration of Ni dopant. The EXAFS was used for the Ni K-edge to probe the local structures of the Ni dopant in ZnO, which show that Ni dopant was substituted for Zn atoms position up to 5at% Ni concentration. [Copyright &y& Elsevier]

Abstract: Structural and optical properties of a-SiN x films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) have been investigated. The Fourier transform infrared (FTIR) spectroscopy shows the structural evolution of the SiN x films, which are defined as Si-rich SiN x and N-rich SiN x films, also confirmed by Raman spectroscopy. The origin of the light emission for SiN x films may be attributed to two mechanisms, i.e., quantum confinement effect (QCE) and transition of defect energy levels. The correlation between light emission and structures of SiN x films is discussed. [Copyright &y& Elsevier]

Abstract: High-quality single-crystal Ga-doped ZnO films have been epitaxially deposited on (0002) sapphire substrate by low-pressure metal organic chemical vapor deposition (MOCVD) technique. The dependence of structural, electrical and optical properties of films on Ga doping concentration was investigated. As grown at the Ga/Zn gas ratio of 3.2at%, the film shows a narrow linewidth of 0.26° for ZnO (0002) peak, high carrier concentration of 2.47×1019 cm−3, and high optical transparency over 90%. The carrier concentration increased sharply and became saturated at higher doping level due to the onset of carrier compensation. The Burstein–Moss blueshift of the absorption edge energy increased as expected with the carrier concentration up to 2.47×1019 cm−3. In addition, doping-induced photoluminescence (PL) emission linewidth broadening and bandgap renormalization (BGR) effects have also been observed. The intensity of PL emission decreased with increasing Ga dopant concentration, which was believed to be a direct consequence of the doping-enhanced nonradiative recombination rates. [Copyright &y& Elsevier]

Abstract: Indium nitride films, grown at 375 °C by low-pressure metal–organic chemical vapor deposition, have been annealed at temperatures ranging from 400 °C to 475 °C under an ambient ammonia atmosphere. According to our X-ray diffraction spectra of the annealed InN films, the integrated intensity of the InN (0002) diffraction peak reaches its minimum value at the temperature of 425 °C, but the full-width at half maximum of the InN (0002) peak shows an opposite change with the annealing temperature. These results indicate that the InN film annealed at 425 °C has the worst structural quality. Scanning electron microscope and X-ray photoelectron spectroscope measurements demonstrate that as the annealing temperature is increased to 425 °C, the density of indium grains on the surface increases greatly due to the volatilization of nitrogen atoms. Above 425 °C, the density of the indium grains begins to decrease, resulting from the desorption of indium. The indium grains formed during this annealing process are then supposed to be responsible for the degraded structural quality in the annealed InN. [Copyright &y& Elsevier]

The ZnO films were grown by low pressure metal-organic chemical vapor deposition (LP-MOCVD) using dimethylzinc (DMZn) and oxygen. The as-grown film has strong (0002) oriented characteristic, containing the chain-like network grains in small sizes, A well-resolved shoulder emission at 3.03 eV in the photoluminescence (PL) spectra has been ascribed to the interstitial zinc in the crystal, implying a serious oxygen deficiency state of the MOCVD growth, in good agreement with the analysis of XPS results. Post-annealing of the films leads to the remarkable improvement of the structure, morphology, components and optical properties. Large hexagonal columnar grains were then observed by atomic force microscope (AFM). The luminescence efficiency was enhanced greatly due to the reduction of the nonradiative defects. Meanwhile, chemisorbed oxygen gives rise to surface acceptor states, resulting in the different radiative recombination. Photoluminescence excitation measurement shows good agreement with the above conclusions. [ABSTRACT FROM AUTHOR]

Abstract: IIIV x N1−x ternary alloys are promising materials for their applications in light-emitting devices in the range of wavelength from ultra violet to the infrared ray due to the large bowing of band gap energy. In this paper, molecular dynamical method was used to calculate the solubility of phosphorus in GaN by using the Gibbs free energy and the dielectric theory. The calculation results show that the content of P in GaN varies with the growth temperature, which may be larger than 25% in the N-rich GaP x N1−x or less than 90% in the P-rich GaP x N1−x , at the growth temperature of about 1500K. We compared our theoretical results with those reported in references. By using light-radiation heating together with low-pressure metal-organic chemical vapor deposition, and ion implantation techniques, we have successfully synthesized N-rich (x &#60;0.17) and P-rich GaP x N1−x (x >0.90) compounds. [Copyright &y& Elsevier]

Abstract: We study the effect of generation and amplification of confined acoustic phonons by drifting electrons in an embedded quantum wire. A general formula for the phonon amplification coefficient α has been derived. Our calculations show that the quantum wire structure can be used for electrical generation of an intense high-frequency coherent phonon flux. The amplification coefficients of the order of cm−1 can be achieved in the sub-THz range for the example of Si0.5Ge0.5 quantum wires embeded in Si. [Copyright &y& Elsevier]

The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the (0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to he 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer. [ABSTRACT FROM AUTHOR]

Mn-doped films were grown in an ammonia-source HVPE system. Mn3GaN0.5 and GaN were detected in film samples without other phase when the HCl–Mn/NH3 ratio range from 1/200 to 1/100. (GaxMn1-x)N phase also formed in films. Two broad bands centered at 305 and 674 cm-1and new peaks at wave numbers of 592 cm-1arised in Raman spectra of Mn-doped films. It was also found that A1(LO) modes of all Mn-doped samples were strongly asymmetric and showed a considerable redshift. Mn-doped films showed an obvious hysteresis loops at room temperature. Mn-doped films showed metallic characteristic and this mixed structure may be greatly beneficial to spin injection magnetotransport devices. [Copyright &y& Elsevier]

Time characteristics have been simulated numerically both for n- and p-channel memory based on Ge/Si hetero-nanocrystals. Owing to the advantages of the staircase potential barrier and the higher band offset on valence band, the retention time of the memory could achieve the increase of several orders while the programming time still hold the same order approximately, compared with the memory based on Si nanocrystals. Therefore, the present memory device would be expected to solve the contradiction between high-speed programming and long retention time. If so, this type of device would be a promising non-volatile memory for future VLSI. [Copyright &y& Elsevier]

ZnO films were prepared on (0002) sapphire by metal-organic chemical vapor deposition (MOCVD) with fixed Zn and O gas flow rates. The film properties displayed complex dependencies on temperature over the range 330–460 °C. All films were preferentially oriented along the (0002) direction and the integrated intensity of the (0002) peak increased with increasing substrate temperature, indicative of an increasing deposition rate. Furthermore, high substrate temperatures promoted the growth of columnar grains, and improved the crystallinity, as the decreasing FWHM of the (0002) ZnO peak suggests. However, it was not the highest temperature sample, but the sample deposited at 390 °C that had the best UV band emission characteristics, with no defect-related luminescence in the photoluminescence (PL) spectra, as well as the highest transmission and sharpest absorption edge in the transmittance spectra. [ABSTRACT FROM AUTHOR]

GaN1−xPx ternary alloys with high P compositions were deposited on sapphire substrates by means of metal-organic chemical vapor deposition. Depth profiles of the elements indicate that the maximum P/N composition ratio is about 17% and a uniform distribution of the P atoms in the alloys is achieved. 2θ/ω XRD spectra demonstrate that the (0 0 0 2) peak of the GaN1−xPx alloys shifts to smaller angle with increasing P composition. From the photoluminescence (PL) spectra, the red shifts to the bandedge emission of GaN are determined to be 73, 78, 100 and 87 meV for the GaN1−xPx alloys with the P/N composition ratios of 3%, 11%, 15% and 17%, respectively. No PL peak related to GaP is observed, indicating that the phase separation between GaN and GaP is well suppressed in our GaN1−xPx samples. [Copyright &y& Elsevier]

Gallium nitride (GaN) epilayers were grown on Si(1 1 1) substrates using nearly polycrystalline α-Al2O3 as the buffer layer by low-pressure metal organic-chemical vapor deposition. The buffer was formed by anodic porous alumina annealed at high temperature. The scanning electron microscope measurement showed that the surface of GaN epilayer was smooth. Simple photoconductive detectors were fabricated with these materials. The spectral response of these detectors exhibited a relatively sharp cutoff near the wavelength of 360 nm and a peak at 340 nm with a shoulder near 360 nm. Under 5 V bias, the responsivities at 340 and 360 nm were measured to be 3.3 and 2.4 A/W respectively. [Copyright &y& Elsevier]

The specific contact resistivity (ρC) and interfacial reaction between Au/Pt/Al/Ti metallic multi-layers and Si-doped n-type AlxGa1−xN (n-AlGaN) layers in modulation-doped Al0.22Ga0.78N/GaN heterostructures have been investigated. By means of the measurements based on the transmission line model, the ρC as low as 1.6 × 10−4 Ω cm2 is obtained. Based on the X-ray diffraction analysis, it is found that N atoms in n-AlGaN layer diffuse out and a much amounts of N-vacancies are formed in n-AlGaN layer near the interface after the sample is annealed at temperatures higher than 500 °C. It induces the heavy n-type doped region in n-AlGaN near the interface, and thus leads to the decrease of the ρC. With increasing the annealing temperature, more N atoms in n-AlGaN layer diffuse out and react with Ti atoms. Ti2N phase is formed at the interface after the sample is annealed at 800 °C. In this case, the ρC further decreases. [Copyright &y& Elsevier]

Tilting in hydride vapor phase epitaxy grown GaN films fabricated by lateral epitaxial overgrowth (LEO) technique has been investigated using four-circle X-ray diffraction measurements and scanning electron microscopy. Both growth rate and V/III ratio influence this tilt. High growth temperatures result in increased wing tilt. For high V/III ratios, above 10.8, a high growth rate is the main factor leading to increased tilt. For V/III ratios below 10.8, a lower V/III ratio decreases the tilt in LEO GaN because of the presence of excess Ga on the growth front resulting in a change of facet direction. Introduction of additional HCl to the surface of the substrate reduces the wing tilt. The mechanism of the influences of these growth conditions on wing tilt was discussed in detail. [Copyright &y& Elsevier]

The Mn-implanted GaN with ferromagnetism at room temperature has been prepared successfully. The optical and structural properties of Mn-implanted GaN films have been investigated. The films studied were grown by metal organic chemical vapor deposition, with Mn implanted in 150 keV, which can offer many distinguished advantages compared with other doping methods. A new energy band with a minimum at 2.9 eV in the reflectance spectra has been observed. The yellow band emission was greatly decreased according to the result of photoluminescence. The results of vibrating sample magnetometer experiment proved the ferromagnetic properties of Mn-doped GaN at room temperature. [Copyright &y& Elsevier]