Mid-infrared optically pumped semiconductor lasers (OPSLs) are presently being investigated for a variety of commercial and military applications. Active regions in such optically pumped lasers must meet the dual requirements of high gain and low loss at mid-IR wavelengths, combined with sufficient absorption of the optical pump at shorter wavelengths for efficient power conversion. In this paper we report the successful growth, fabrication, and characterization of high-performance OPSLs that employ novel active regions consisting of combinations of GalnAsSb integrated-absorber layers with type-II GaInSb/InAs quantum well regions. With 1.85-µm optical pumping at 85 K, OPSLs with such active regions have exhibited a peak output power of 2.1 W at 3.9 pm, improved beam quality, power conversion efficiency of ∼8%, and characteristic temperatures of ∼47 K.

Calculations of optoelectronic properties for superlattice materials require accurate subband energies, wavefunctions and radiative matrix elements. We have recently begun using a solution method based on the Empirical Pseudopotential Method, or EPM. This method shows particular strength in analyzing structures with short periods or thin layers, for which the standard method, based on k,p perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the method for applications to superlattice structures. Finally, we will apply the EPM method to several type II superlattice samples and compare the predictions to absorbance spectroscopy data.

We present the first reported MBE growth of light emitting diodes (LED's) with active regions made up of InSb/ InNxSbl−x (O<x<0.02) superlattices, grown onto InSb(100) substrates. Such dilute alloys of nitrogen in other III-V materials have been shown to exhibit very large bandgap bowing parameters due to differences in atomic size and the electro-negativity of nitrogen. Novel growth techniques have been developed to enable epitaxy of high quality InNxSbl−x, using an electron cyclotron resonance (ECR) plasma source. Material characterisation was performed by double crystal x-ray diffraction (DXRD) and transmission electron microscopy (TEM), and nitrogen composition has been determined using DXRD and secondary ion mass spectrometry (SIMS). To determine the effect of nitrogen on bandgap, the structures have been fabricated into LED's with InSb/InNxSbl−x superlattice active regions with period ∼1100A. For a nitrogen content of ∼0.3%, the peak emission of the diodes shifts from ∼6pm to >71µm at room temperature.

The linewidth enhancement factor is a fundamental parameter that characterizes the limit of spectral purity and the tendency for filamentation in a semiconductor laser. For either narrow-line or high-power operation, it is generally desirable that the linewidth enhancement factor be minimized. This parameter depends primarily on the shape of the differential gain spectrum of the active region material. In mid-infrared laser materials, band structure engineering has been used routinely to minimize the effects of nonradiative recombination. This same approach can be used to tailor the differential gain spectrum of these materials to minimize the linewidth enhancement factor.

Favorable features of the electronic structure of the material include 1) band-edge dispersion in the conduction band which shifts the peak of the gain away from the band edgeCand 2) intersubband absorption resonances, which can be designed to lie above the peak gain in energy. Both of these strategies shift the peak of the differential gain closer to the peak gain, and thus reduce the linewidth enhancement factor. These electronic structure design strategies can be used to reduce the linewidth enhancement factor in type-II InAs/GaInSb systems to almost 1.0, which is significantly smaller than typical values of 2.5–5 in type-I strained quantum wells. We note that a linewidth enhancement factor close to 1 is much smaller even than a typical linewidth enhancement factor in visible or near-infrared semiconductor lasers. Furthermore in some materials the peak of the differential gain lies in a region of positive gain, indicating that a grating could be used to select a mode with negligible linewidth enhancement factor.

We report the recent progress in type-II interband cascade (IC) lasers, For the 4.2-pm devices, lasing was observed up to 210 K, and the threshold density was only 95 A/cm2at 90 K and 284 A/cm2at 200 K. For the 4.5-μm lasers, the internal loss was only 11.6 cm−1 and the internal quantum efficiency was 460% at 90 K. We have also demonstrated the first dual-wavelength type-II IC lasers at 4.482 and 4.568 μm.

We report on room temperature cw operation of type-I semiconductor quantum well (QW) laser diodes based on the GaInAsSb/AIGaAsSb/GaSb material system emitting beyond 2.2 µm. Lasing is observed in cw mode up to at least 320 K. A high internal quantum efficiency of 65% and a low internal loss coefficient of 5 cm1have been achieved for a single QW (SQW)large optical cavity laser at 280 K. An extrapolated threshold current density for infinite cavity length of 144 A/cm2and 55 A/cm2has been deduced for the 3 QW and SQW lasers, respectively, which scales with the number of QWs. A maximum cw light output power of 230 mW at 280 K heatsink temperature was obtained for a 3 QW large optical cavity laser with HR/AR coated mirror facets, mounted substrate-side down.

We report the growth of InSb on GaAs using InAISb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of ∼0.55µm thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron mobilities of ∼40,000 cm2/V.s. We have investigated the In1−xAlxSb buffers for compositions x≤0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

Compound semiconductors find extensive application as magnetic position sensors in the automotive environment. Typical applications involve the sensor element, a permanent magnet attached to the sensor, and a moving magnetic circuit -a target wheel. Wider mechanical gaps in the magnetic circuit can be utilized with a sensor of higher sensitivity, and thus high sensitivity is valuable. Further limitations on the choice of materials are imposed by temperature sensitivity, as the automotive environment is characterized by wide temperature operating ranges (-40°C up to 200°C). The magnetic signal may be hidden by the temperature drift in the sensor output, andthus temperature stability limits the sensor's resolution. Automotive position sensors find use in ignition timing and misfire detection (cam and crank sensors), as wheel speed sensors (anti-lock brakes and other types of active wheel-control), in brushless electric motors and several other applications. This work reviews progress achieved to refine the use of InSb for automotive sensing applications.

A strong correlation between the surface step structure and phase separation in metastable GaInAsSb epitaxial layers grown by organometallic vapor phase epitaxy has been identified. The full width at half maximum (FWHM) of 4-K photoluminescence (PL) peak energy is used as a semi-quantitative measure of the degree of phase separation. The step structure of GaInAsSb grown at 525 °C is vicinal, while it is step-bunched for layers grown at 575 °C. The corresponding 4-K PL FWHM data indicate that the degree of phase separation is minimized when the layers aregrown at the lower growth temperature. It is proposed that the longer terrace lengths of a step-bunched surface are associated with a longer adatom lifetime compared to a vicinal surface, and thus the adatoms have more time to cluster and phase separate, which is the preferred equilibrium state. Increasing the growth rate, which reduces the adatom lifetime, also reduces the PL FWHM, and thus, the degree of phase separation.

This paper reports on the design and fabrication of GaSb/n-InxGal1−xAsySb1−y/p-AlxGal−xAsySb1−y heterojuction photodetectors operating in the 2 - 2.4 µm wavelength region. Device structures were grown by LPE and fabricated as mesa-type diodes by RIE etching in CC14/H2 plasma. For mesa passivation a surface treatment in (NH42S water solution was carried out. The photodiodes structures are characterized by differential resistance RoA=400 ωcm2. Measured detectivity is in the range 3.1010 - 2. 1011 cmHz1/2/W, in dependence on the active area and cutoff wavelength.

W lasers based on type-II antimonides were recently operated nearly to room temperature under the conditions of cw optical pumping. However, the development of electrically pumped mid-infrared lasers has not yet reached the same level of performance. This is largely related to the more challenging task of simultaneously optimizing the doping/transport and gain/optical properties of the devices. Here we report a demonstration of type-II mid-IR diode lasers employing W active quantum wells. Laser structures with 5 or 10 active periods sandwiched between broadened-waveguide separate confinement regions and quaternary optical cladding layers were processed into 100-µm-wide stripes, cleaved into 1-mm-long cavities, and mounted junction side down. For 0.5-1 µs pulses at a repetition rate of 200 Hz, lasing was obtained up to a maximum operating temperature of 310 K, where the emission wavelength was 3.27 µm. The threshold current densities were 110 A/cm2and 25 kA/cm2 at 78 and 310 K, respectively. The characteristic temperature, To, was 48 K for temperatures between 100 and 280 K. Operation in cw mode was obtained to 195 K, with threshold current densities of 63 A/cm2and 1.4 kA/cm2at 78 and 195 K, respectively, with To = 38 K between 78 and 195 K. Significant further improvements in the operating characteristics are expected once the optimization of the designs and fabrication procedures is complete.

The interband cascade lasers (IC) represent a new class of mid-IR light sources, which take advantage of the broken-gap alignment in type-II quantum wells to reuse electrons for sequential photon emissions from serially connected active regions. Here, we describe recent progress in InAs/GaInSb type-II IC lasers at emission wavelengths of 3.8-4 µm; these semiconductor lasers have exhibited significantly higher differential quantum efficiencies and peak powers than previously reported. Also, these lasers were able to operate at temperatures up to 217 K, which is higher than the previous record (182 K) for an IC laser at this wavelength. We observed from several devices at temperatures above 80 K a slope efficiency of ∼800 mW/A per facet, corresponding to a differential external quantum efficiency of /500%. A peak optical output power exceeding 4 W/facet and peak power efficiency of /7% were observed from a device at 80 K. Also, we report the first cw operation of IC lasers.

Type-II InAs/GaInSb superlattices of different designs have been grown by molecular beam epitaxy on wafer bonded InGaAs on GaAs, and on standard GaSb substrates. The extremely thin (∼100Å) InGaAs layer is loosely bonded to the GaAs substrate and serves as a compliant layer for subsequent epitaxy of a larger lattice constant material. The effects of these substrates on the optical, electrical, and structural properties of the superlattice were studied. The superlattices grown on bonded substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb. The photoresponse results for the superlattices on the bonded 2 inch diameter substrates, with the InGaAs compliant layer, were not as favorable as early work on similar, smaller area, bonded substrates. However, refinements to the wafer bonding process to eliminate microvoids between the bonded layers will provide higher quality superlattices.

We have developed 65 GHz Wide Bandwidth InGaAs Photodiodes and Photoreceivers for optical fiber driven telecommunication applications. The Photodiode operates at a nominal reverse bias of -3V and has a minimum responsivity of 0.5 A/W at 1300 and 1550 nm wavelength. The Ripple Factor is less than ± dB for a wide band of frequencies, DC to 50 GHz. The salient feature of the PIN is an on-chip co-planar waveguide output for proper impedance matching. We have also designed Ultra Wide Bandwidth Amplifiers using InGaAs p-HEMT technology and monolithically integrated them with InGaAs Photodiodes. These Opto-electronic Integrated Circuits (OEICs) which combine optical, microwave, and digital functions on the same chip is a technology that has significant potential for commercial applications such as ethernet fiber local area networks and optical communications systems (Synchronized Optical Network SONET, ISDN, telephony and digital CATV). Important inter-service military applications are optically fed phased array systems and optically controlled microwave networks for airborne and spaceborne systems.

Progress in the development of ion implantation enhanced quantum well shape modification as a technique for monolithically integrating optoelectronic devices of varying functionalities is reviewed. Fundamental issues related to the physics of the technique, both material issues and device issues, are considered and the performance of both discrete and integrated devices is discussed. The main conclusion of this review is that there are no inherent drawbacks to the utilization of this technique and some serendipitous advantages but that more work on reproducibility and reliability is required to ensure commercial viability.

We report on the realization of distributed feedback quantum cascade lasers in the GaAs/AIGaAs material system. The use of a metallized surface relief grating for feedback allows a fabrication process without regrowth. A feature of this laser is that either single mode or double mode emission at λ ≍ 10 µm is achieved, which is typical for index coupled lasers. The coupling coefficient is measured from the mode spacing for double mode emission of a strong overcoupled laser to be κ ≍ 24 cm"−1. The emission wavenumber can be continuously tuned with the temperature at a rate of dv / dT ≍ 0.048 cm−1/K, which is in close agreement to the temperature dependence of the refractive index of GaAs.

We have designed and fabricated a quantum dot infrared photodetector which utilizes lateral transport of photoexcited carriers in the modulation-doped A1GaAs/GaAs two-dimensional (2D) channels. A broad photocurrent signal has been observed in the photon energy range of 100–300 meV due to bound-to-continuum intersubband absorption of normal incidence radiation in the self-assembled InAs quantum dots. A peak responsivity was as high as 2.3 A/W. The high responsivity is realized mainly by a high mobility and a long lifetime of photoexcited carriers in the modulation-doped 2D channels. Furthermore, we found that this device has high operation temperature and very high photoconductive gain.

Time-resolved photoluminescence spectroscopy has been used to investigate carrier decay dynamics in InxGa1−xAs1−yNy (x ∼ 0.03, y ∼ 0.01) epilayers grown on GaAs by metalorganic chemical vapor deposition. Time-resolved PL measurements, performed for various excitation intensities and sample temperatures, indicate that the broad PL emission at low temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07–0.34 ns are measured; these photoluminescence lifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of the decay lifetime at 10 K, whereby the lifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations. We have also studied the effects of post-growth rapid thermal annealing (RTA) on the integrated photoluminescence emission intensity, which indicate that the optimal annealing conditions is 690 °C when annealed for 120 seconds in a nitrogen ambient.