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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 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.

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.

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.

It is well known that Al 2 O 3 scale adherence to aluminide bond coats is enhanced by Pt alloying additions, however, the actual mechanisms of the Pt effect are not defined. Both NiAl and NiPtAl bond coats were fabricated on two types of single-crystal superalloys (de-sulfurized and nominal S content) by a high-purity chemical vapor deposition (CVD) process. Oxide scale adherence to CVD NiAl during thermal cycle testing to 1150°C was dramatically improved by reducing both superalloy and coating S impurities. Platinum additions to CVD aluminides resulted in significant further improvements in scale adherence, especially on the higher-S superalloy. The most obvious manifestation of the Pt effect was elimination of large voids at the oxide-metal interface. Transmission electron microscopy of α-Al 2 O 3 scales after isothermal exposure indicated internal void growth on both NiAl and NiPtAl, but scales on NiPtAl also contained Hf from the superalloy. These results further support previous observations that Pt mitigates the detrimental effect of S impurities by modifying the driving force to stabilize or accelerate void growth, although this may not be the only beneficial effect.

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.

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.

GaN (Gallium nitride) has been grown successfully on sapphire by RF plasma MBE through optimizing the growth condition. Two dimensional triple axis mapping (TDTAM) was used to characterize the GaN epilayers. The dislocation density in the epilayers was estimated to be about 7.8×108 cm−2 according to the mosaic model. The 77K photoluminescence (PL) of the Si-doped GaN with different concentration show that Si can act both donor and acceptor at very high concentration. Transmission spectrum has also been measured for further understanding of the sample.

GaN epilayers of about 1 μm thick were grown directly on 6H–SiC(0 0 0 1)substrates by direct current plasma assisted molecular beam epitaxy. High-resolution X-ray diffraction and two-dimensional triple axis mapping were used to characterize the GaN epilayers. A FWHM of 11.9 arcmin for an ω scan and 1.2 arcmin for an ω /2 θ scan were observed. A careful study of the rocking curves showed that there were some large mosaics in the GaN epilayers. The two dimensional triple axis mapping showed that the GaN mosaics were disoriented in the (0 0 0 1) plane but rather uniformed in the direction perpendicular to the plane. A mosaic model was deduced to explain the phenomenon, and the dislocation density was estimated to be about 2×10 9 cm −2 according to the model.

Inductively coupled plasma (ICP) etching of GaSb, AlGaAsSb, and InGaAsSb using BCl 3 /Ar plasma discharges was investigated for the fabrication of GaInAsSb/AlGaAsSb/GaSb laser diodes. Etching rates and selectivity were characterized as functions of gas flow ratio, accelerating voltage, and ICP source power, and the etching mechanism was discussed in detail. It is observed that the etch rate of GaSb and AlGaAsSb is much higher than that of InGaAsSb. The etched surfaces of GaSb, AlGaAsSb all have comparable root-mean-square roughness to the unetched samples over a wide range of plasma conditions; however, it is much rougher in etching of InGaAsSb. The selectivity between GaSb and AlGaAsSb was close to unity over the entire range of plasma conditions investigated, which is desirable for the fabrication of quaternary antimonide laser diodes.