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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.

We present a novel method to characterize the internal quantum efficiency and internal optical loss of semiconductor lasers. Its basic concept is studying the dependence of the external quantum efficiency on the mirror reflectivity. This method is very different from the conventional one, which focuses on the external quantum efficiency as a function of cavity length. Our method has great advantages, such as the capability of measuring the internal quantum efficiency and optical loss of a single laser diode, which is intrinsically impossible by the conventional method.

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 .

The effects of bismuth on the performances of InP-based detectors and multiple triangular quantum wells in 2–3 µm band have been investigated. The cut-off wavelength of the InGaAsBi detector is tailored to 2.1 µm by the bismuth incorporation in the absorption layer, but the detector still shows an encouraging dark current due to decreased lattice mismatch to InP substrate. The material quality of the InAs/InGaAs triangular quantum wells has been significantly improved by introducing bismuth as a surfactant during growth. The moderate bismuth reduces the surface roughness, improves the heterostructure interfaces and enhances the photoluminescence intensity obviously, whereas deterioration occurs in the case of excessive bismuth flux. Bismuth shows a promising potential to improve InP-based detector and laser structures both by incorporating into the alloys and acting as a surfactant.

Integrated, compact, and economical pulse driving and TE control modules for pulsed quantum cascade lasers (QCL) have been developed. Based on those modules, an effective tunable diode laser spectroscopy (TDLS) setup has been constructed for the evaluation of pulsed QCL and demonstration of TDLS concepts. Connecting our mid-infrared QCL module to the driving module using cable of 10 Ω characteristic impedance results in down chirp light pulses suitable for intrapulse scheme of TDLS; a usable down chirp of about 0.78 cm−1 is achieved for current pulse with 240-ns pulse width. Connecting the QCL module to the driving module using stripline of characteristic impedance

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.

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.

The thermal characteristics of antimonide ridge waveguide MQW lasers have been investigated numerically and experimentally, and compared with phosphide lasers in detail. Using the finite-element method, the heat accumulation and dissipation process of the lasers under CW and pulse driving conditions have been simulated, and quantitative thermal time constants were introduced to describe the cooling efficiency of the lasers. The non-uniform temperature distribution inside the active core of the laser and its effects on lasing spectra have been discussed, and confirmed by the measurement of the broadening of the lasing spectrum towards the blue side. A way to improve the thermal property of antimonide lasers have also been proposed and discussed.

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.

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 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.

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 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.

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 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.

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.

Al/sub 0.52/In/sub 0.48/P-Ga/sub 0.51/In/sub 0.49/P-GaAs photovoltaic detectors using GaInP as the light absorption layer and AlInP as the widow layer have been fabricated by using gas source molecular beam epitaxy, and their performance has been characterized in detail. The detectors show infrared-blind and ultraviolet-enhanced features and have good response in visible band, which makes them a good candidate in certain applications. Excellent performance has been demonstrated on the detectors, a resistance area product of R/sub 0/A=1.3/spl times/10/sup 8/ /spl Omega//spl middot/cm/sup 2/, and an open-circuit voltage of V/sub oc/>1.05 V have been measured at room temperature.

We report room temperature low current density of InP-based AlInAs/InGaAs quantum cascade laser (QCL). For a 7.66-mum QCL, the threshold current density of 1.7 kA/cm2 at 300 K, pulsed output power of 800 mW at 80 K, and continuous-wave (CW) output power of 13 mW at 135 K are achieved. An 8.91-mum QCL comprised 100 stage active region operating up to 320 K in pulsed mode also presented.

We report on the improved performance of InAlAs-InGaAs-InP metal-semiconductor-metal photodetectors (MSMPDs) with graded superlattice structure grown by gas source molecular beam epitaxy. Low dark current density of 0.75 pA//spl mu/m/sup 2/ at 10-V bias, high-breakdown voltage of >40 V at 10 /spl mu/A and fast transient response of /spl sim/16 ps (t/sub r/, FWHM and t/sub f/) at 5-V bias have been obtained.

InGaAsSb/GaSb detector is very promising for novel applications in long-wavelength range (>2 /spl mu/m). Dark current, composed of surface and volume currents, is a leading source of the electronic noise. Due to a large density of surface states of the InGaAsSb surface, the surface recombination current is the dominant factor in the whole dark current. In this paper, the influence of alkali and neutralized (NH/sub 4/)/sub 2/S passivation on the dark current density of InGaAsSb PIN detector has been studied. A new modified neutralized (NH/sub 4/)/sub 2/S passivation method was proposed. Results show a drastic improvement of the device characteristics was obtained by the modified neutralized (NH/sub 4/)/sub 2/S passivation. In our experiment, the PIN detectors were taken from the same epitaxial wafer and prepared by same fabrication process. In order to compare the effect of different (NH/sub 4/)/sub 2/S passivation solution, the devices were divided into two groups. The results indicate that the sulfur-passivation can remove native oxide and depress surface stats of InGaAsSb effectively.

We report on the growth, characterization and performance of compressively strained In/sub 0.75/Ga/sub 0.25/As/InGaAsP (/spl lambda//sub g/=1.3 /spl mu/m) MQW structures on InP substrates for laser diodes in the 2.0-2.1 /spl mu/m range. These laser wafers were grown by gas source molecular beam epitaxy (GSMBE) for the first time. Both broad area and ridge-waveguide structure lasers have been fabricated and evaluated. The electrical and optical properties of high quality InGaAsP, corresponding to the band wavelength of 1.3 /spl mu/m, have been investigated in detail. The properties of InGaAsP layers have a sensitive dependence on the growth temperature. With the optimization of growth conditions, high quality InGaAsP layers with narrow double-crystal X-ray diffraction rocking curve (DCXRC) and PL FWHM, and high Hall mobility have been obtained. The EL at room temperature of broad-area InGaAs/InGaAsP strained MQW laser structures have shown a peak wavelength of 1.98 /spl mu/m, indicating the precise control of material composition and layer thickness. Pulsed lasing at 77 K has been achieved under an injection current of 70 mA for the ridge waveguide structure of laser diodes and the FWHM of the spectrum is 5.3 nm with peak at 1.816 /spl mu/m.

This work reports on InAs/In0.53Ga0.47As strain compensated quantum well structures on InP-based metamorphic buffer to generate the type-I emission of beyond 3 μm. The metamorphic buffer is composed of InxAl1−xAs graded layer and In0.8Ga0.2As virtual substrate layer. Atomic force microscope, transmission electron microscope and x-ray diffraction measurements show the moderate surface and structural properties. A photoluminescence signal up to 3.05 μm has been achieved at 300 K, which is one of the longest wavelengths from the interband emission of InP-based antimony-free structure. It is promising to employ this quantum well structure on metamorphic buffer for the laser demonstration with emission around 3 μm.

In this paper, we report the growth of device quality InGaAs/InAlAs/InP materials by gas source molecular beam epitaxy (GSMBE) and their applications to HEMTs and MSM-PDs. Larger conduction band discontinuity and larger electron mobility which led to improved electrical performance of HEMT materials and devices can be obtained by adoption of dual strained InGaAs channel layer and InAlAs Schottky layer.