Recently, mid-infrared diode lasers fabricated from the antimonide-based III-V compounds have been receiving increased attention for potential applications in trace gas detection, spectroscopy, pollution monitoring, and military systems. In this paper we will report the growth, fabrication, and modeling of high performance diode lasers with wavelengths longer than 3 μm. Molecular beam epitaxy (MBE) has been employed for the growth of these Type-I, strained quantum-well (QW) laser structures on GaSb and InAs substrates. The lasers consist of compressively strained InAsSb wells, tensile-strained InAlAsSb barriers, and lattice-matched AlAsSb cladding layers. QW lasers grown on GaSb substrates, with emission wavelengths of ∼3.9 μm, have operated pulsed up to 165 K. At 80 K, cw power of 30 mW/Facet has been obtained. Ridge-waveguide lasers have operated cw up to 128K. QW lasers grown on InAs substrates have emission wavelengths between 3.2 and 3.55 μm. Broad-stripe lasers on InAs have exhibited cw power of 215 mW/facet at 80 K, pulsed threshold current density as low as 30 A/cm2 at 80 K, characteristic temperatures (TO) between 30 and 40 K, and maximum pulsed operating temperature of 225 K. Ridge-waveguide lasers on InAs have cw threshold current of 12 mA at 100 K, and a maximum cw operating temperature of 175 K. In this paper we will present some of the key issues regarding the MBE growth, fabrication, and modeling of such lasers and discuss future directions for improved device performance.

We report metalorganic chemical vapor deposition-grown double heterostructure and multiple quantum well InAsSb/InAsSbP laser diodes emitting at 3 to 4 μm and light emitting diodes up to 5 μm. Maximum output power up to 1 W (from two facets) with differential efficiency above 70 % up to 150 K was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.6 μm at 90 K. Maximum operating temperature up to 220 K with threshold current density of 40 A/cm2 at 78 K were achieved from the double-heterostructure lasers emitting at 3.2 μm. The far-field beam divergence as narrow as 24° was achieved with the use of higher energy gap barrier layers, i.e., lower effective refractive index, in MQW active region. We also discuss the effect of composition-fluctuation in the InAsSb active region on the gain and threshold current of the lasers.

Mid-infrared lasers grown by MOCVD with ALAsSb claddings and strained InAsSb active regions are reported. A 3.8–3.9 μm injection laser with a pseudomorphic InAsSb multiple quantum well active region lased at 210 K under pulsed operation. A semi-metal layer acts as an internal electron source for the injection laser. An optically pumped laser with an InAsSb/InAsP strained-layer superlattice active region was demonstrated at 3.7 μm, 240 K.

We review recent applications of wavefunction engineering to the design of antimonide quantum heterostructures with favorable properties for infrared devices. Examples include electro-optical and all-optical modulators based on Г-L intervalley transfer, type-II quantum well lasers with enhanced gain per injected carrier, and type-II interband cascade lasers predicted to combine low thresholds and high output powers.

Mid-infrared (3–5 μm) infrared lasers and LEDs are being developed for use in chemical sensor systems. As-rich, InAsSb heterostructures display unique electronic properties that are beneficial to the performance of these midwave infrared emitters. We have grown AlAs1−xSbx epitaxial layers by metal-organic chemical vapor deposition using trimethylamine (TMAA) or ethyldimethylamine alane (EDMAA), triethylantimony (TESb) and arsine. We examined the growth of AlAsl−xSbx using temperatures of 500 to 600 °C, pressures of 70 to 630 torr, V/III ratios of 1–27, and growth rates of 0.3 to 2.7 μm/hour in a horizontal quartz reactor. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction are utilized as a source for injection of electrons into the active region of lasers. A regrowth technique has been used to fabricate gain-guided lasers using AlAs1−xSbx for optical confinement with either a strained InAsSb/InAs multi-quantum well (MQW) or an InAsSb/InAsP strained layer superlattice (SLS) as the active region. Under pulsed injection, the InAsSb/InAs MQW laser operated up to 210K with an emission wavelength of 3.8–3.9 μm. Under pulsed optical pumping, the InAsSb/InAsP SLS operated to 240K with an emission wavelength of 3.5–3.7 μm. LED emission has been observed with both active regions in both p-n junction and semi-metal injection structures.

Liquid phase epitaxy can be effectively used to grow a thick graded ternary or quaternary buffer layer to provide a “virtual substrate” for subsequent device epitaxy. Grading characteristics of InGaAs, InAsSb and InAsSbP epitaxial layers grown by LPE are discussed. The effects of the principal LPE growth parameters on epiiayer thickness, surface morphology and composition, lattice-mismatch and photoluminescence efficiency were investigated and are described.

Gai1−xInxASySb1-y (0.06 < x < 0.18, 0.05 < y < 0.14) epilayers were grown lattice-matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy (OMVPE) using triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony. These epilayers have a mirror-like surface morphology, and exhibit room temperature photoluminescence (PL) with peak emission wavelengths (λP,300K) out to 2.4 μm. 4K PL spectra have a full width at half-maximum of 11 meV or less for λP,4K < 2.1 μm (λP,300K = 2.3 μm). Nominally undoped layers are p-type with typical 300K hole concentration of 9 × 1015 cm−3 and mobility ∼ 450 to 580 cm2/V-s for layers grown at 575°C. Doping studies are reported for the first time for GalnAsSb layers doped n type with diethyltellurium and p type with dimethylzinc. Test diodes of p-GalnAsSb/n-GaSb have an ideality factor that ranges from 1.1 to 1.3. A comparison of electrical, optical, and structural properties of epilayers grown by molecular beam epitaxy indicates OMVPE-grown layers are of comparable quality.

A large number of 4 inch (100 mm) diameter 1–2 μm thick InSb films have been grown on GaAs by low pressure metalorganic chemical vapor deposition (MOCVD) turbo disk technology. Raman scattering microscopy was used to study the effects of III-V source ratios on the film crystalline quality and to optimize the growth parameters. Multi-point Raman measurements over the entire 4” wafer were performed to exhibit the uniformity distribution of the film crystalline quality. A FTIR reflectance mapping system has been established to map the film thickness distribution. Good uniformity of the film thickness and crystalline perfection was obtained. Raman and FTIR are showing useful tools for non-destructive characterization of large area wafers for industrial mass production.

Semiconducting antimonide compounds have received increasing attention as the alternative materials for mid-infrared photonic devices, with a variety of applications such as remote sensing, pollution monitoring, and molecular spectroscopy. For many, if not all these devices it is necessary to pattern antimonide films into mesa or line structures. While plasma etching techniques have played an increasing role in producing such features, little was reported until now on dry etching of GaSb- and AlSb-containing alloys. In this paper we present the results of our recent work towards the development of the technology for GaSb-based ridge wave-guide laser emitting at 2–2.3 μm at RT. Specifically, we discuss the fabrication of double-channel mesa structure in AlxGai1−xAsySb1−y/GaSb (x=0.2–0.5) heterostructure materials by RIE technique. The effects of gas and material composition, rf power, pressure and temperature on etching characteristics were studied with special attention paid to surface quality, etching rate and etching profile, which are crucial for obtaining a single mode waveguide. CCI2F2/H2 and CCI4/H2 process chemistries were investigated which shows the latter to provide vertical sidewalls and residue free etch surfaces at controllable etch rates.

Arsenic-rich InAs/InAs1−x Sbx strained-layer superlattices (SLS's) are studied in time-resolved optical, and CW magneto-optical spectroscopies. A pronounced type-II offset, with electrons confined to the alloy layers, is found. High radiative efficiencies at wavelengths well into the mid-IR, and the suppression of Auger recombination yield LED's operating at 3–10 μm. Present room temperature powers are ∼30 μW, probably limited by inadequate carrier confinement.

In this paper, we report on the growth and fabrication of InSb detectors and Focal Plane Arrays (FPA's) on (100) Si, Al203, and (100) and (111) GaAs substrates for infrared (IR) imaging. Several advantages result from using GaAs, Si, or Al203. First, InSb FPA's on these materials do not require thinning as with detectors fabricated from bulk InSb. In addition, these substrates are available in larger sizes, are semi-insulating (GaAs and sapphire), and are less expensive than InSb.

Optimum growth conditions have been determined and discrete devices have been fabricated on each substrate material. The structural, electrical, and optical properties were verified using x-ray, Hall, photoresponse, and photoluminescence (PL) measurements. Measured x-ray Full Widths at Half Maximum (FWHM) were as low as 55 and 100 arcsec for InSb epilayers on GaAs and Si, respectively. Hall mobilities were as high as 128,000, 95,000 and 72,000 cm2/V-sec at 200 K, 77 K, and room temperature, respectively. In addition, 77 K PL linewidths were as low as 18, 20, and 30 meV on GaAs, Si, and sapphire substrates respectively, well below the 48 meV value previously reported in the literature.

In collaboration with Lockheed Martin Fairchild Systems (LMFS), IR thermal imaging has been obtained from InSb FPA's on GaAs and Si substrates. This is the first successful IR thermal imaging from heteroepitaxially grown InSb. Because of the high quality substrates, larger areas, and higher yields, this technology is very promising for challenging traditional InSb FPA hybrid technology.

We will present calculations of the ideal performance of mid-infrared InAs/InGaSb superlattice quantum well lasers. For these systems several periods of an InAs/InGaSb type-II superlattice are grown in quantum wells. Calculations of the non-radiative and radiative lifetimes of the carriers utilize the full non-parabolic band structure and momentum-dependent matrix elements calculated from a semi-empirical multilayer K · P theory. From these lifetimes, threshold current densities have been evaluated for laser structures. We find serious problems with the hole and electron confinement in the superlattice quantum wells grown to date, and propose a four-layer superlattice structure which corrects these problems.

(Al, In)GaAsSb/GaSb MQW lasers with a broadened waveguide have been used to fabricate 2-μm diode lasers with CW output power of 1.2 W. 2-μm linear arrays have output powers of 11 W and an efficiency of 0.13 W/A.

Three types of structures were fabricated using molecular beam epitaxy. High-resolution x-ray diffraction measurements demonstrated the high structural quality of InSb/AlxIn1−xSb superlattices grown on InSb and GaAs substrates. Hall effect data revealed the effect of substrate temperature on autocompensation in InSb δ-doped with Si. Two-dimensional electron systems with a high mobility were realized in InSb quantum wells with AlxIn1−xSb barriers δ-doped with Si.

We report on the optimum growth conditions for Molecular Beam Epitaxy (MBE) growth of InSb onto InSb (111)A and (111)B substrates. It was found that for (111)A substrates the optimum epilayer morphology was obtained for growth temperatures above 385°C and with a Sb:In ratio of 1.5:1. In contrast, for the (111)B surface, best morphology was found for growth temperatures above 385°C but with V:III ratio of ∼7.0:1. In both cases the dopant incorporation was found to be the same as the (100) surface and did not particularly depend either on V:III ratio or substrate temperature. We also describe the device characteristics of InAlSb light emitting diodes (LEDs) grown lattice matched onto ternary InGaSb(111)A substrates using the optimized growth conditions obtained.

We have investigated the mid-infrared spontaneous and stimulated emission between confined subbands in the conduction band of GaAs/AlGaAs quantum wells. The carriers which give rise to the intersubband emission are excited in the upper subbands using an intersubband optical pumping in coupled asymmetric quantum wells. The quantum wells are designed using phonon engineering in order to obtain population inversion between the second and first excited subband. This is obtained by adjusting the subband energy spacing between E2 and E1 close to the optical phonon energy which in turn allows an efficient relaxation. We have first observed intersubband spontaneous emission between E3 and E2 at 14 μm using an intersubband pumping with a CO2 laser in resonance with the E1-E3 transition. In a second set of experiments, the quantum wells are embedded in an infrared waveguide. We have measured the stimulated intersubband gain using a picosecond two-color free electron laser. The first color bleaches the E1-E3 transition and provides the population inversion. The intersubband stimulated gain is measured versus the waveguide length and photon energy. Stimulated gains ≈ 80 cm−1 are reported thus demonstrating that laser emission under optical pumping appears feasible in optimized structures. Finally, we show that intersubband emission can also be observed in quantum wells using an interband optical pumping.

We theoretically study the absorption in grating coupled quantum wells in a cavity. We describe the coupling betwen the three oscillators present in the structure: The intersubband transition, the grating and cavity modes. We show that optical mode anticrossings should be observed. The splitting between the cavity mode and the intersubband transition is calculated but its experimental observation would require electronic coherence times longer than what was measured.

In this paper, light emitting diodes (LEDs) are used to study the recombination dynamics of minority electrons in p type InAs. The LEDs operate through injecting electrons into p type material with a free surface. When surface recombination is dominant, the output of the LEDs is shown to depend only on the strength of the radiative recombination and not on its efficiency. When surface recombination is not dominant, the dependence of the LED efficiency on the thickness of the active layer is analysed to give the minority carrier diffusion lengths and recombination efficiencies. the electron diffusion lenSgth is shown to be 3±0.5 μm in 5×10−18 cm−3 p type InAs and 6±1 pm in 2×10 cm−3 p type material. An upper limit of∼2.1×10−28 cm6 s−1 is deduced for the total Auger recombination rate constant in p type material.

The different possible geometries for intersubband transitions in microcavities are discussed. A consequence of the selection rule governing intersubband transition is the vanishing interaction with the electromagnetic field inside a usual vertical cavity. The geometry of vertical planar cavities which has been used extensively with interband transitions is therefore useless in the case of intersubband transitions. Different solutions are reviewed to overcome this problem. The breakdown of the selection rule in a vertical cavity is first discussed. This can be done with the use of vertical quantum wells, or thanks to intracavity diffraction gratings. Second, the use of in plane cavities is discussed. Two solutions are here envisaged: Whispering gallery modes in microdisk cavities, and efficient etched air/GaAs Bragg mirrors. Concerning the latter attractive solution, the losses by diffraction into the substrate are evaluated theoretically and experimentally. The solution of the Maxwell equations by a finite element method in this three dimensional system shows the great importance of diffraction. These results are confirmed by waveguided Fourier transform spectroscopy. To overcome this difficulty, we propose the use of lower refractive index substrates, such as oxidized AlAs.

Vertical-cavity surface-emitting lasers (VCSELs) with suitable interdiffusion quantum wells profile by the use of selective impurity-induced disordering is proposed for high power single mode operation in large area devices. It is shown that the transverse optical confinement in the quantum well active region formed by the diffusion profile counteracts the influence of carrier spatial hole burning for VCSELs biased at high injection current Results indicate that a single mode operation can be maintained in VCSELs with the diameter of core region equal to 50μm.