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InP- and GaAs-based metamorphic In 0.83 Ga 0.17 As photodetectors were grown and investigated. Compared to InP-based photodetector, the dark current of GaAs-based photodetector at room temperature increased 2–3 times but still comparable, whereas at 77 K the dark current increased 2–3 orders. The deep-level transient spectroscopy results reveal that a deep level trap state exists in the GaAs-based photodetector structure. The higher dark current in GaAs-based photodetector at low temperature was mainly ascribed to a deep level trap induced tunneling current. The deep trap centers can also induce non-radiative recombination with smaller thermal active energy in the GaAs-based photodetector structure.

The effects of well shapes and waveguide materials on InP-based InAs quantum well lasers have been investigated. The laser structures were grown on metamorphic In 0.65 Al 0.35 As buffers. A novel trapezoidal quantum well composed of In y Ga 1−y As grading and InAs layer was used to improve the quality of quantum well. Quaternary In 0.65 Al 0.2 Ga 0.15 As waveguide was applied instead of ternary In 0.65 Ga 0.35 As to enhance the carrier injection. The material qualities have been characterized by X-ray diffraction, transmission electron microscopy and photoluminescence measurements, while the device properties of the lasers with various structures were investigated at different temperatures. Results show that the laser performances have been improved by the use of trapezoidal quantum wells and InAlGaAs waveguides.

The effects of well widths and well numbers of InGaAs triangular quantum well lasers in 2.30–2.44 μm range using antimony-free material system on InP substrates are investigated. The triangular quantum well was equivalently formed by using gas source molecular beam epitaxy grown InAs/In0.53Ga0.47As digital alloy and the pseudomorphic growth was confirmed by the X-ray diffraction measurements. Lasing at 2.30 μm above 330 K under continuous wave operation has been achieved for the laser with four 13 nm quantum wells. By increasing the well width to 19 nm, the continuous wave wavelength has been extended to 2.44 μm at 290 K, whereas the epitaxial quality and laser performances are deteriorated. For those lasers with well width up to 19 nm, the moderate reduction of the quantum well numbers can restrict the strain accumulation and improve the laser performances. Continuous wave lasing at 2.38 μm above 300 K has been achieved.

The impact of buffer schemes on the strain relaxation and structural characteristics of In 0.83 Ga 0.17 As photodetector structures with relatively high lattice mismatch (5.9%) grown on GaAs substrate by gas source molecular beam epitaxy has been investigated. Reduction of surface roughness, full widths at half maximum of X-ray diffraction signals and threading dislocations, as well as an enhancement of photoluminescence intensity were observed for the In 0.83 Ga 0.17 As photodetector structure with fixed-composition In 0.83 Al 0.17 As buffer compared to those with continuously graded In x Al 1− x As buffer. The role of fixed-composition In 0.83 Al 0.17 As buffer layer is investigated, and it is believed that a couple monolayers of In 0.83 Al 0.17 As at the initial growth stage can provide high density of nucleation site by the formation of quantum dots at the interface and thus to reduce the strain energy caused by the large lattice mismatch between In 0.83 Al 0.17 As and GaAs.

InP-based high indium content In 0.83 Ga 0.17 As photodetector structures with lattice mismatch up to 2.1% have been grown by gas source molecular beam epitaxy system. The photodetectors using continuously graded and step-graded In x Al 1−x As buffer structures were grown and demonstrated. The effects of the buffer scheme were investigated by the measurements of atomic force microscopy, high-resolution X-ray diffraction, photoluminescence and device performance. Results show that the full relaxation of the photodetector structure has been achieved by using continuously graded InAlAs buffer. Superior optical properties and lower dark currents can be reached for the photodetector structure with continuously graded buffer layer.

InAlGaAs photodiodes with 50% cut-off wavelength of 1.41 μm at room temperature have been grown by using gas source MBE with convenient and reliable procedure, and the performances have been characterized in detail. The InAlGaAs absorption layer shows a mismatch of −8×10 −5 to the InP substrate with a full width at half maximum of around 20 arcs. Dark current of 247 pA at reverse bias of 10 mV and zero bias resistance of 41 M Ω has been measured for the devices at room temperature with 200 μm mesa diameter. The dark current of this InAlGaAs photodetector is about 20 times lower than the In 0.53 Ga 0.47 As photodetector with similar structure processed at the same time.

A variety of metamorphic InGaAs photodetector structures have been grown on InP substrates by gas source molecular beam epitaxy. Their characteristics have been measured by atomic force microscopy, X-ray diffraction and photoluminescence to investigate the effects of growth temperature, grading profile and digital alloy intermediate layers in the buffer. The growth temperature is optimized to linearly decrease during the growth of In x Al 1− x As graded buffer, and kept at a relatively high temperature to grow the InGaAs absorption layer. The linearly grading profile of the composition in the buffer is superior to the convex grading profile, which indicates that the grading rate in the beginning could not be too high. The insertion of digital alloy intermediate layers in the In x Al 1− x As buffer improves the structural and surface qualities of the photodetector structures, whereas it introduces some negative effects on the optical quality.

Effects of the injector doping densities on lasing properties of mid-infrared InAlAs–InGaAs–InP quantum cascade lasers at 4.3 μm have been studied. Lasers with different average injector doping between 1.29E17 cm −3 and 2.07E17 cm −3 have been grown by gas source molecular beam epitaxy (GSMBE), and their lasing characteristics were investigated. Lasers with low doped injectors (1.68E17 cm −3 ) exhibited lower threshold current density, longer emission wavelength and lower characteristic temperature T 0 . The lower injector doping density decreases waveguide loss. On the other hand, the high doping of the injector increases heat transfer through phonon in QCL active region, and thus results in high characteristic temperature T 0 .

Wavelength-extended In y Ga 1− y As photodiodes with cut-off wavelengths of 2.0, 2.4 and 2.7 μm at room temperature were grown using gas source molecular beam epitaxy with linearly graded In x Al 1− x As ( x =0.52 to y ) buffer layers and In y Al 1− y As cap layers. A convenient and reliable correlating ramping procedure was developed for the growth. Detector performances were compared with our standard homojunction detectors containing linearly graded In x Ga 1− x As buffer layers. The heterojunction detectors showed better performance than the homojunction detectors. Also, the use of wider bandgap buffer and cap made the heterojunction detectors more suitable for both front and back illumination. For the photodiodes with 500 μm mesa diameter at room temperature, the typical dark current ( V R =10 mV) and R 0 A were 74 nA and 104 Ω cm 2 at 290 K for the cut-off wavelength of 2.4 μm. Optimization of the buffer structure was necessary for further extension of the response wavelength.

A group of AlInGaAs/InGaAs/InAs strain compensated triangular quantum well samples have been grown by using gas source molecular beam epitaxy (GSMBE), and their properties are investigated by X-ray diffraction and photoluminescence (PL) measurements. Through the adjustment of the growth temperature and barrier width, the quality of the quantum wells has been improved distinctly. The maximal PL peak wavelength of 2.38 μm at 300 K has been reached. The X-ray diffraction measurements show good structural properties and the full-width at half-maximum (FWHM) of PL spectrum is 17 meV at 12 K and 33 meV at 300 K. For the sample with larger well width, the transition involving the second sub-energy levels occurs.

We have investigated the growth of InAs/GaSb type-II superlattices by gas-source molecular-beam epitaxy, where Sb cracker cell and AH 3 high-temperature injector are used to provide Sb and As flux, respectively. Sharp InAs/GaSb interfaces can be obtained at optimized growth conditions, revealed by high-resolution transmission electron microscopy. Moreover, it was found that the intrinsic net tensile strain of the InAs/GaSb superlattices can be partially compensated by intentional insertion of a sub-monolayer InSb layer at the interfaces of InAs and GaSb. Finally, based on InAs/GaSb superlattices grown by gas-source molecular-beam epitaxy (GSMBE), we have fabricated a photodiode with cut-off wavelength of 4.9 μm.

A set of room temperature low threshold current densities of a mid-infrared InP-based quantum cascade lasers (QCLs) have been demonstrated. Threshold current densities as low as 1.7 kA/cm2 for multi-mode Fabry-Perot QCLs at an emission wavelength of 7.6 μm and 0.9 kA/cm2 for single-mode distributed feedback QCLs at an emission wavelength of 7.7 μm have been achieved at 300 K. The results obtained are through the precision control of doping incorporation and concentration, the active region of the structure for suppressing the current leakage, and the low resistance material choice in the wave guide cladding and plasmon for improving heat dissipation.

The ternary wide bandgap AlInP alloys have been grown on GaAs substrates by using gas source molecular beam epitaxy, and the relationship between various growth parameters and the composition, lattice mismatch, surface morphology as well as doping concentration of the AlInP epi-layers have been investigated in detail. The AlInP epi-layer with lattice mismatch of +4.3 × 10−4 and full-width at half-maximum of X-ray diffraction peaks of 21.6″ and 14.9″ for epi-layer and substrate respectively have been obtained. The maximum reachable p and n type carrier concentration for Be or Si doping were found to be around 1 × 1018 and 5 × 1018 cm−3 respectively around lattice match composition.

We have demonstrated the first Gas source molecular beam epitaxy (GSMBE) grown distributed feedback quantum cascade laser (DFB QC-laser) laser with low threshold current density operation at 7.6 μm. High quality DFB QC-laser heterostructures were grown by an one step GSMBE growth procedure. The first-order grating was defined by a holographic technology. A tunable single mode DFB QC-laser operation in pulsed mode with a low threshold current density of 574 A/cm 2 and a peak optical power of 50 mW at 70 K and 7.6 μm have been obtained. The side mode suppression ratio and the maximum single mode wavelength tuning range by changing their heat sink temperature are 23 dB and 20 nm, respectively.

The heat management of the AlGaAsSb/InGaAsSb ridge waveguide MQW laser at 2 μm wavelength range has been investigated by using the finite-element method (FEM). Results show that the thermal behavior of antimonide lasers is quite different from InP or GaAs-based lasers mainly due to the low thermal conductivities of antimonides, which are coincident with the observed results. By using junction down-mounting or using thick gold plating layer as heat spreader on the top contact for substrate down-mounting, the thermal characteristics of the antimonide lasers can be dramatically improved.

In this paper, we report results on the material quality of InGaAs/AlInAs lattice-matched to InP and the performance of a Fabry–Perot QC lasers grown by gas-source molecular beam epitaxy using a one-growth step procedure. The surface defect density of epi-layer with 10/cm 2 over a 2′′ diameter wafer are achieved. The Fabry–Perot QC lasers uncoated exhibit operation in quasi-continuous-wave at room temperature with a low threshold current density of 1.75 KA/cm 2 and 7.95 μm. The emitting wavelength is in good agreement with the predicted emission wavelength by design.

Enhancement-mode (E-mode) operation In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs PHEMTs were designed for high performance and were successfully grown by gas source molecular beam epitaxy (GSMBE). An optimized GSMBE growth process based on the memory effect studied has been applied to precisely control the InGaP/InGaAs and InGaP/GaAs interface quality and composition. The lattice mismatch of 10 −4 and composition uniformity of better than ±0.2% for 3″ diameter InGaP/GaAs layers were obtained. E-mode operation InGaP/InGaAs PHEMTs and related low-noise amplifier (LNA) circuits were obtained. The E-mode PHEMT had a threshold voltage near 0 V and the LNA can operate under a single-voltage supply of 1.5–3.0 V and at 2.5 GHz with a gain of over 20 dB and a noise figure ( N f ) of 3.43 dB.

Alkali and neutralized (NH 4 ) 2 S passivation treatment effects on the performance of MBE-grown InGaAsSb/GaSb PIN detectors have been studied. Results show the dark current density under −0.5 V bias decreased from 1.01 mA/cm 2 to 490 μA/cm 2 for alkali (NH 4 ) 2 S solution treatment and 87 μA/cm 2 for neutralized (NH 4 ) 2 S solution treatments, respectively. A modified neutralized (NH 4 ) 2 S passivation method for GaSb-based antimonide devices has been proposed. The XPS spectra indicated that (NH 4 ) 2 S passivation can suppress oxidization and form Ga–S and In–S bonds on the InGaAsSb surface.

A mid-infrared laser characterization system, including a gpib programmable I–P and I–V set-up based on direct waveform measurement with extraordinary wide pulse duration and duty cycle tuning range, in conjunction with a Fourier transform infrared spectroscopy system adapted with double modulation technique, has been developed. Based on this characterization system, the characteristics of gas source MBE grown InAlAs/InGaAs/InP quantum cascade lasers (QCL), especially their thermal property, have been evaluated. The results show that in the combination of I–P, I–V and spectral measurements at various driving pulse parameters, the thermal resistance, lasing conditions as well as spectral characteristics of the mid-infrared QCL could be deduced. This characterization system is also a useful tool for the evaluation of other types of diode lasers in the mid-infrared band.

Al 0.52 In 0.48 P photovoltaic detector has been fabricated using gas source molecular beam epitaxy and its characteristics have been measured in detail. The Al 0.52 In 0.48 P absorption layer shows a mismatch of +4.76×10 −4 to the GaAs substrate with a full width at half maximum of 22.5 arcsec. The dark current is only 0.78 pA at reverse bias of 500 mV and the R 0 A is about 1.7×10 8 Ωcm 2 at room temperature. The measured peak responsivity at zero bias is 0.287 A/W at 470 nm with 50% cut-on and cut-off wavelengths at 440 and 495 nm, respectively.

Two micron AlGaAsSb/InGaAsSb multiple quantum well lasers were grown by solid source molecular beam epitaxy. To avoid strain relaxation in active region, 10 periods multiple quantum well samples with different barrier widths were carefully analyzed. We find that a 15 nm wide barrier is best for Al 0.2 Ga 0.8 As 0.02 Sb 0.98 /In 0.24 Ga 0.76 As 0.05 Sb 0.95 quantum wells. Five-micron wide ridge waveguide lasers were fabricated. A slope change in power–current characteristics was observed. The emission wavelength switches from 2.01 (corresponding to 1e–1hh transition) to 1.87 μm (corresponding to 2e–2hh transition) as the slope changes.

Lasers with emission wavelength of 1.8–2.1 μm offer many important applications to laser spectroscopy, eye-safe medical care and trace chemical detection. Strained InGaAs/InGaAsP structures on InP substrates have been reported as an alternative approach for the development of semiconductor laser diodes in the spectral range 1.8–2.1 μm due to the superior InP substrate quality and mature processing technology. In this paper we report the fabrication and performances of InGaAs/InGaAsP/InP strained quantum well lasers grown by gas source molecular beam epitaxy. The diodes show good I – V characteristics, and the typical turn-on voltage at room temperature is around 0.4–0.5 V. A threshold current of about 120 mA is achieved for a chip with 500 μm cavity length and 4.5 μm stripe width. The maximum output power with 10% duty cycle is 18 mW. The main peak of the laser spectrum is located at 1.84 μm.

In this paper we report for the first time gas-source molecular beam epitaxy of both n- and p-channel InGaP/(In)GaAs modulation-doped heterostructure. The sheet density dependence of the two-dimensional hole gas (2DHG) mobility of p-type In 0.49 Ga 0.51 P/GaAs structures was investigated by Van der Paul Hall measurement at 300 and 77 K. The 2DHG densities of 2.78×10 12 and 1.02×10 12 cm −2 with mobilities of 191 and 2831 cm 2 /V s at 300 and 77 K, respectively, for In 0.49 Ga 0.51 P/GaAs structures have been achieved. Low-temperature and high-magnetic field Hall measurements were also carried out. Longitudinal resistance of the structure shows two oscillations with different periods at a temperature of 0.3 K, indicating that two subbands have been occupied by holes in the GaAs channel. The sheet density for each subband was estimated to be 1.22×10 12 and 0.77×10 12 cm −2 , respectively. Both high hole mobility transistors (HHMTs) and high electron mobility transistors (HEMTs) were demonstrated. HHMTs show a maximum DC transconductance of 35 mS/mm. The saturation current is 57 mA/mm at 300 K with V d =−3 V. Both extrinsic transconductance and saturation current of our novel In 0.49 Ga 0.51 P/GaAs HHMTs are well improved, compared with those of AlGaAs/GaAs and InGaAs/GaAs HHMTs. Enhanced-mode InGaP/InGaAs pseudomorphic HEMTs were achieved with a maximum DC transconductance of 250 mS/mm.

In this paper, we present the results of the calculation and design for waveguide and the dependence on the performance of mid-infrared InAlAs/InGaAs/InP quantum cascade (QC) lasers grown by gas source molecular beam epitaxy. The dispersion of refractive indices are calculated by taking into account the contribution of the free-carrier concentration absorption. We also report the first GSMBE grown InAlAs/InGaAs/InP QC lasers emitting at 5.1mm, operated in pulse mode up to 130 K with T0 of 208 K and J0 of 2.6 kA/cm 2 . For the QC laser designed with lower waveguide cladding InP concentration of 1 � 10 18 cm � 3 , it does not lase. Presented theoretical and experimental results indicate that the free-carrier absorption in both upper InGaAs contact layer and lower InP waveguide cladding does play an important role in the dispersion of the index of refraction of semiconductors at mid–far-infrared wavelengths and influence the performance of QC lasers. # 2001 Elsevier Science B.V. All rights reserved.

Strain compensated 1.3 μm InAsP/InGaAsP laser structures have been grown by using gas source MBE and the ridge waveguide laser diodes have been fabricated. The temperature characteristics of those laser chips have been investigated in detail. The ridge type laser chips show threshold current about 10 mA at room temperature, with slope efficiency greater than 0.35 W/A/un-coated facet. The characteristic temperature of the threshold current were greater than 90 K from 25°C to 90°C. The spectral and far field characteristics of those laser chips also have been investigated.

Two micron wavelength InGaAsSb/AlGaAsSb multi-quantum well laser structures have been grown by using solid source MBE, and ridge type diode laser chips with narrow ridge width have been fabricated. The performance of this MBE grown 2 μm wavelength lasers have been evaluated on chip level without chip mounting and wire bonding. The laser chips show a threshold current of about 75 and 123 mA at 0°C and 40°C, respectively, with a characteristic temperature T 0 of 79 K. Maximum output power was greater than 25 mW per uncoated facet below 40°C, with no observable kink. Maximum lasing temperature greater than 80°C has been achieved in quasi-CW driving conditions. Fairly good single mode lasing characteristics have been observed under pulsed driving condition in 0–60°C range, with a temperature tuning coefficient of 0.78 nm/°C.

Lattice-matched N–p + –n In 0.49 Ga 0.51 P/GaAs heterojunction bipolar transistors (HBT's) with heavily beryllium doped base and undoped spacers were grown by gas source molecular beam epitaxy (GSMBE). The epitaxial structure consists of, from the bottom to the top, a 5000 A n + -GaAs sub-collector with Si doping level of 3×10 18 cm −3 , a 7000 A n-GaAs collector doped at concentration of 3×10 16 cm −3 , a 60 nm p + -GaAs base with Be doping level up to 3×10 19 cm −3 inserted between two undoped GaAs spacers, a 100 nm N-In 0.49 Ga 0.51 P emitter doped at 3×10 17 cm −3 . The structure was completed with a 150 nm n + -GaAs cap layer with Si doping level of 3×10 18 cm −3 . Devices with emitter area of 100×100 μm were fabricated on the grown wafer by using selective wet chemical etching technique and photolithographic process. AuGeNi/Au was used for the emitter and collector contacts, and Cr/Au was used for the base contact. The turn-on voltages of p + -GaAs/N-In 0.49 Ga 0.51 P heterojunction and p + -GaAs/n-GaAs junction are 1.0 and 0.65 V. The reverse breakdown voltages of the B–E and B–C junctions are 10 and 12 V. The common-emitter current-voltage characteristics show that the maximum current gain reaches 320 at the collector current of 90 mA.

We report on the growth of two types of GaInAsSb detector structures by solid source molecular beam epitaxy. One structure is capped with an AlGaAsSb window layer, and the other is a conventional PIN detector. The fabrication and performance of detectors are also reported. As a result of suppression of surface recombination, the dark reverse saturate current for the detector capped with window is much lower than the other type of detector. Black body detectivity D bb * of the detector with an AlGaAsSb window is 5.0×10 8 cm Hz 1/2 /W, and voltage responsivity R v is 78 V/W at 300 K. For detectors without window, D bb * is 5.1×10 8 cm Hz 1/2 /W, and R v is 37 V/W at 300 K. Relative spectral response is also measured. The peak response wavelength is 2.19 μm at room temperature.

The growth and characterization of GaInAs/AlInAs triple quantum well structures are reported. The structures are characterized with high-resolution X-ray diffraction combined with high-resolution simulation based on the dynamical theory of X-ray diffraction and with photoluminescence. The good agreement in both peak position and intensity of the high-resolution X-ray diffraction spectra with the high-resolution simulation reveals the precise control of the epilayer thickness and the good quality of interfaces. The photoluminescence spectra are analyzed concerning the peak position, interface roughness, and lineshape. These three aspects correlate well with each other, and the interface roughness is determined by fluctuations of 1 monolayer occurring every 3 effective exciton radii in the lateral plane.

The precise growth controls of strained AlInAs and GaInAs for strain-balanced quantum cascade lasers (QCLs) are optimized and developed. The precise measurements of constituent compositions and thicknesses of strained AlInAs and GaInAs are performed on the strain-balanced AlInAs/GaInAs superlattice (SL). The doping incorporation behaviour of strained AlInAs and GaInAs is studied. High-crystalline quality QCL structures with desired two-dimensional electron gas (2DEG) densities in the injector region are achieved through precise composition, thickness and doping controls.

The range of miscibility is calculated in the frame of delta lattice parameter (DLP) model by taking into account the effects of strain and relaxation. The numerical results show that decreasing the epilayer thickness causes the range of miscibility to become narrower and finally to disappear as the epilayer thickness decreases. The results of thick epilayers are in agreement with models which do not include strain energy.

In this paper we show the evaluated results of a quantum cascade laser (QCL) structure with a vertical transition and a Bragg reflector grown by gas source molecular beam epitaxy (GSMBE). The Al 0.48 In 0.52 As/Ga 0.47 In 0.53 As QCL structures lattice matched to the InP substrate consists of alternating 25 periods of undoped coupled-quantum-well active regions with compositionally graded layers, a superlattice graded region to provide strong electron confinement in the upper state using a Bragg reflector and an InP buffer layer. The laser operates in the temperature range from 8 to 250 K with measured integrated optical powers up to 70 mW at 8 K, and 5 mW at 250 K. The high-resolution emission spectrum of the laser at 250 K provides direct evidence of laser action from the narrowing of the strong line and clearly illustrating the longitudinal mode structure.

In this paper, we report novel In 0.49 Ga 0.51 P/(In)GaAs/GaAs high-hole mobility transistor structures with different p-channel and doping methods. Electrical and optical properties of the grown structures were investigated by Van der Pauw Hall measurement and low-temperature photoluminescence. The current-voltage characteristics were performed on field effect transistors with T-shaped gates. By using delta-doping technique, 2DHG densities of 2.78 ×10 12 and 1.02 x 10 12 cm - 2 with mobility of 191 and 2831 cm 2 /V s at 300 and 77 K for In 0.49 Ga 0.51 P/GaAs structures have been achieved. For In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs structures, 2DHG densities increased to 2.84×10 12 and 1.29 ×10 12 cm -2 with mobility increasing to 208 and 2972 cm 2 /V s at 300 and 77 K, respectively. Photoluminescence spectra of In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs modulation doped heterostructure shows a peak located at 1.310 eV, which is attributed to a transition from V 3/2 band to conduction band. The processed high-hole mobility transistors have a maximum extrinsic transconductance of 35mS/mm and a maximum saturation current of 57mA/mm at 300 K.

In 0.49 Ga 0.51 P/(In)GaAs/GaAs heterostructure is an excellent candidate for two dimensional hole gas (2DHG) system as it had a large valence band offset ratio. In this paper we reported the growth of In 0.49 Ga 0.51 P/(In)GaAs/GaAs p-type modulation doped heterostructures by gas source molecular beam epitaxy. Electrical and low temperature photoluminescence properties of structures with different p-channels and doping methods were investigated. Hole mobilities of 131 cm 2 /V s at 300 K and 2020 cm 2 /V s at 77 K for a homogeneity doped GaAs channel structure were obtained. By using delta-doping technique, hole mobilities of 191 cm 2 /V s at 300 K and 2831 cm 2 /V s at 77 K were achieved. The Hall mobilities could be still slightly enhanced when using pseudomorphic InGaAs channel instead of GaAs channel. The change of hole mobilities were qualitatively explained by the ionized impurity scattering mechanism.

Temperature-dependent photoluminescence properties of n-type GaSb/AlSb superlattices are reported. The measurements at temperatures ranging from room temperature to 4 K and with various excitation powers show that for our samples, radiative recombination dominates the recombination process at low temperatures, and very strong exciton–phonon coupling is found from the linewidth analysis. The best fit of the integrated photoluminescence intensity as a function of temperature shows that the quench of the photoluminescence at high temperature is due to the thermal activation of nonequilibrium electrons from the Γ1toL1subband.

Molecular beam epitaxial growth and characterization of GaInAsSbAlGaAsSb strained multiple quantum wells (MQWs) have been investigated. Optimization for the growth have been studied by characterizing the MQWs with double-crystal X-ray rocking curve, photoluminescence (PL) and absorption measurements and evaluating laser diode performance. Up to the fifth-order the satellite peak is resolved in rocking curves, and asymmetric distribution of satellite peaks is found which indicates large strain in quantum well structures. PL and absorption measurements at different temperatures show the high quality of GaInAsSbAlGaAsSb multiple quantum wells grown under optimized conditions. The full-width of half-maximum of a PL peak as narrow as 9.0 meV is achieved at 4 K, and room-temperature PL and well-resolved excitonic absorption peaks are observed in the MQW structures. By using the GaInAsSbAlGaAsSb MQWs as active layers in laser diodes, pulsed operation at room temperature with emission at 2.05 μm has been obtained.

Modulation-doped In x Ga 1 − x As/In y Al 1 − y As/InP heterostructures have been grown with a diffusion pumped V80H gas source molecular beam epitaxy system. Their electrical properties have been studied with Hall measurements. The effects of spacer layer thickness and buffer layer structure (InAlAs or InAlAs + InP) on lattice-matched and pseudomorphic In x Ga 1 − x As/In y Al 1 − y As/InP 2DEGs and HEMTs characteristics have been investigated in detail. Crystalline and interface qualities can be improved by adding an InP buffer layer before the InAlAs buffer, resulting in an improvement in material electrical properties. A thicker spacer layer will cause a decrease of electron gas density and an increase of electron mobility. Adopting strained channel and Schottky layers can dramatically improve material electrical performance. For InGaAs/InAlAs/InP pseudomorphic 2DEG (P-2DEG) structures, electron mobilities of 11 230 cm 2 /V · s at n s of 2.3 × 10 12 cm −2 at 300 K and 6.52 × 10 4 cm 2 /V · s at n s of 2.1 × 10 12 cm −2 at 77 K were obtained and μ of 9273 cm 2 /V · s at 3.6 × 10 12 cm −2 and 4.5 × 10 4 cm 2 /V · s at n s of 3.1 × 10 12 cm −2 for both strained InGaAs channel layers and InAlAs Schottky layers in P-HEMT structures were achieved.

High quality InP layers with a good surface morphology, a high electron mobility (μ = 112041 cm2/V · s at 77 K), a low background carrier concentration (n = 1.17 × 1014cm−3at 77 K) and a narrow photoluminescence spectrum width (FWHM = 1.5 meV at 5 K) have been obtained by using gas-source molecular beam epitaxy (GSMBE) through the optimization of the growth conditions. The effects of the growth conditions on the quality of InP grown by GSMBE are demonstrated and discussed.

Molecular beam epitaxy has been employed to grow Ga x In 1− x As 1− y Sb y PIN detectors operating at 2.0 to 2.6 μm on (100)-oriented GaSb substrates. The epitaxial layers were characterized by X-ray double-crystal diffraction, Fourier transform infrared spectroscopy, electron microprobe analysis, and Hall effect measurements. The background hole concentration and mobility at room temperature are (4–5) × 10 16 cm −3 , 254 cm 2 /V·s and 9 × 10 15 cm −3 , 970 cm 2 /V·s for GaInAsSb and GaSb, respectively. For a PIN mesa front-illuminated photodetector, a maximum external quantum efficiency of 65% without anti-reflection coating and a peak detectivity D λ ∗ at 2.5 μm of 3.0 × 10 9 cm Hz 1/2 / W with a cut-off wavelength of 2.6 μm at room temperature have been achieved.

Electrical properties and donor ionization energy level E D in Te-doped n-Al x Ga 1-x As 0.003 Sb 0.97 (0

High-resistivity and p-type ZnSe-based II–VI semiconductor superlattices were prepared by molecular beam epitaxy on (100) GaAs or (100) InP substrates. The modulation-doped ZnSe-ZnTe superlattice by using antimony as a dopant has a hole concentration of 5×10 14 cm -3 . The absorption spectra of undoped ZnSe-ZnS superlattices were measured at temperatures ranging from 16 K to room temperature and three absorption peaks corresponding to 1E-1HH, 1E-1LH and 1E-3HH transitions were observed for the first time. Two absorption peaks corresponding to the transitions of the first heavy-hole and light-hole to the conduction band were also observed in the room temperature absorption spectra of ZnSe-ZnTe superlattices.