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There is a need for semiconductor junctions with very low leakage for energy conversion from low level radioactive or radio‐luminescent sources, and low noise blue‐green photodiodes. We report the properties of two types of GaP junctions; a Schottky barrier of Pd on liquid phase epitaxy grown n‐type GaP and a p+ over n junction grown by metal‐organic chemical vapor deposition. Both types of junctions show very low leakage currents and good efficiency for power conversion from low level beta particles, x rays, and blue‐green light.

High concentrations of recombination‐promoting impurities in the near‐surface region of a semiconductor can produce virtually complete suppression of carrier‐driven photochemical etching processes. In‐diffusion of Zn to levels appropriate for ohmic contact formation on GaAs (mid‐1020/cm3) has been employed to reduce etching to an undetectable level in n‐GaAs with n=1.0×1017 and 1.3×1018/cm3 and to produce a greater than ten‐fold reduction in etching of semi‐insulating GaAs. Raman spectroscopy of the altered near‐surface region shows enhanced electronic scattering, which indicates the presence of a sufficient impurity concentration to suppress etching. Transmission electron microscopy shows the near‐surface region to be crystalline without significant numbers of defects following Zn diffusion. Possible applications of this process include self‐aligned etching of transistor and laser structures.

Lasers and light-emitting diodes with multistage, type I InAsSb/InAsP quantum well active regions are reported. These ten stage, cascaded devices were grown by metalorganic chemical vapor deposition. The broadband light-emitting diodes produced high average powers, >2 mW (∼80 K, 3.7 μm) and >0.1 mW (∼300 K, 4.3 μm). A 3.8–3.9 μm laser structure operated up to T=180 K. At 80 K, peak power >100 mW and a slope efficiency of 48% (4.8% per stage) were observed in our gain guided lasers. The slope efficiency was strongly dependent on cavity length, and analysis of efficiency data suggests an internal differential quantum efficiency >1 and a loss coefficient ⩾100 cm−1.

In situ optical reflectance transients reveal that the morphology evolution of the initial low-temperature buffer layer strongly influences the structural and electrical quality of the high-temperature GaN films. Moreover, the morphology evolution of that buffer layer, specifically evolution of the spatial and orientational distributions of the nuclei, is strongly affected by H2. The growth conditions for which surface smoothness is maintained throughout the two-step growth do not necessarily produce the best quality final GaN films; instead, there may be an optimal roughness and incubation period en route to the best quality final films.

The properties of InAsSb/InAsP strained-layer superlattice (SLS), midwave infrared materials, and devices are reported. SLSs were grown by metal-organic chemical vapor deposition and characterized by magnetophotoluminescence and x-ray diffraction. Excellent performance was observed for an SLS light emitting diode (LED) and an optically pumped SLS laser. The semimetal injected, broadband LED emitted at 4 μm with 80 μW of power at 300 K and 200 mA average current. The laser displayed 3.86 μm emission at 240 K, the maximum operating temperature of the laser, and a characteristic temperature of 33 K.

Gain‐guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/InAs multiquantum well active region were grown by metalorganic chemical vapor deposition. 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 the laser. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8–3.9 μm. We also report on the two‐color emission of a light‐emitting diode with two different active regions to demonstrate multistage operation of these ‘‘unipolar ’’ devices.

A pseudomorphic, compressively strained InAs0.94Sb0.06 multiple quantum well injection laser, emitting in the 3.5–3.6 μm range is reported. The device was grown by metalorganic chemical vapor deposition, and x‐ray and optical characterization indicate that the active region has a very low dislocation density. In pulsed mode, the laser operated at 135 K and displayed a characteristic temperature of 33 K, equaling the highest value reported for molecular‐beam epitaxy grown, InAsSb/InAlAsSb active region lasers of comparable wavelength. Factors limiting the performance of these lasers are discussed.

AlSb and AlAsxSb1−x epitaxial films grown by metalorganic chemical vapor deposition were successfully doped p‐ or n‐type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500 ° C and 76 Torr using trimethylamine alane and triethylantimony. AlAs0.16Sb0.84 films lattice matched to InAs were grown at 600 ° C and 76 Torr by adding arsine. Secondary ion mass spectroscopy showed C and O levels below 2×1018 and 6×1018 cm−3, respectively, for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn‐doped AlAs0.16Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between 1×1017 to 5×1018 cm−3 for Zn‐doped material and electron concentrations in the low to mid‐ 1018 cm−3 for Sn‐doped material.

Interband magnetophotoconductive spectroscopy was used to determine the reduced masses of several optical transitions in an InAs1−xSbx/In1−xGaxAs strained‐layer superlattice and a superlattice constituent, InAs1−xSbx alloy (x≊0.1). In both the alloy and the superlattice, light and heavy hole transitions were identified. From the light‐heavy hole splitting in the superlattice, we estimate the valence band offset and find type I behavior. Effective masses and band gap energy are measured for the CuPt ordered alloy.

Heterostructures with biaxially compressed, As‐rich InAsSb are being investigated as active regions for midwave infrared emitters. InAs1−xSbx/In1−xGaxAs (x≊0.1) strained‐layer sublattices (SLSs), nominally lattice matched to InAs, were grown using metalorganic chemical vapor deposition. An SLS light‐emitting diode was demonstrated which emitted at 3.6 μm with 0.06% efficiency at 77 K. Optically pumped laser emission at 3.9 μm was observed in a SLS/InPSb heterostructure. The laser had a maximum operating temperature of approximately 100 K.

We use absorption, photoluminescence, and x‐ray diffraction spectra of two GaAs/AlAs type II heterostructures, whose GaAs well thicknesses differ by ≂4 A to obtain a direct measurement of the individual quantum confinement energy shifts of the heavy hole, light hole, and electron levels. We find that excitonic absorption linewidths are dominated by inhomogeneous broadening that arises from half‐monolayer well‐thickness fluctuations. For self‐consistency these shifts are applied to separately determine the individual valence‐band and conduction‐band offsets.

The thermal interdiffusion of AlSb∕GaSb multiquantum wells was measured and the intrinsic diffusivities of Al and Ga determined over a temperature range of 823–948 K for 30–9000 s. The 77-K photoluminescence (PL) was used to monitor the extent of interdiffusion through the shifts in the superlattice luminescence peaks. The chemical diffusion coefficient was quantitatively determined by fitting the observed PL peak shifts to the solution of the Schrodinger equation, using a potential derived from the solution of the diffusion equation. The value of the interdiffusion coefficient ranged from 5.2×10−4 to 0.06nm2∕s over the conditions studied and was characterized by an activation energy of 3.0±0.1eV. The intrinsic diffusion coefficients for Al and Ga were also determined with higher values for Al than for Ga, described by activation energies of 2.8±0.4 and 1.1±0.1eV, respectively.

We have characterized the effects of Be+ implantation and controlled‐atmosphere annealing on the structure of Ga(AsP)/GaP strained‐layer superlattices (SLSs). Damage and strain distributions within the implanted layers were examined by cantilever‐beam bending measurements, double‐crystal x‐ray rocking curves, and a variety of ion‐channeling techniques. Implantation‐induced displacement damage produces additional stress in the SLS, in this case reaching 4.5×109 dyn/cm2, a value comparable to that of the built‐in stresses in these SLSs. The depth distribution of ion damage as measured by ion channeling agrees well with the predictions of the trim code, although substantial recovery occurs during the room‐temperature implant. Rocking curve analysis indicates that the interlayer strain in the SLS is retained despite the ion damage, and that the ion damage can be modelled as an independent additional source of strain in the as‐implanted structure. The linear expansion of the layers due to point defect generati...

We have investigated the properties of Ga(AsP)/GaP strained‐layer superlattices (SLSs) that have been doped by implantation of 1×1015/cm2, 75 keV Be+ followed by controlled‐atmosphere annealing at 825 °C for 10 min. Our results indicate that doping of these strained‐layer superlattices without disordering is a viable process. Liquid‐helium temperature photoluminescence suggests a binding energy for the implanted acceptors of 50 meV, consistent with that of beryllium in GaP‐based alloys. The implantation‐doped regions exhibit room‐temperature electrical activation of 15% and hole mobilities of 20 cm2/V s, consistent with the values expected for type‐converted GaP‐based alloys. SLS diodes fabricated by this process exhibit excellent rectification properties, with a forward turn‐on voltage of approximately 1.8 V and low values of room‐temperature reverse leakage current densities. Diodes formed from SLSs with original n‐type doping of 1×1017/cm3 have typical reverse leakage current densities of 1×10−7 A/cm2 ...

We have examined the properties of (InGa)As/GaAs strained‐layer superlattices (SLSs) that have been disordered by implantation of 5×1015/cm2, 250 keV 64Zn+ followed by controlled atmosphere annealing at 680 °C for 30 min. Ion channeling techniques indicate that the Zn‐disordered regions of the SLS contain extensive crystalline damage after annealing. Simulations of the disordering process using an analytic ion range code predict that the electrical junction resulting from the implantation process is located outside the disordered region of the SLS in both the vertical and the lateral directions. Junction electroluminescence intensity for given drive current densities from the Zn‐disordered SLS devices is comparable to that from reference Be‐implantation‐doped (SLS retained) devices and greatly exceeds that from heavily dislocated grown‐junction mesa diodes in the homogeneous alloy of the average SLS composition; this result is consistent with the results of the simulations. This study demonstrates that im...

The vaporization and sublimation reactions for the ytterbium fluoride system have been investigated by mass loss, x‐ray powder diffraction, elemental analysis, and mass spectrometry. When YbF2.00 is heated in vacuum, it decomposes to give a metal rich vapor and a metal deficient residue until the composition YbF2.40(4) is reached. The following equilibrium reactions were established: YbF2.40(s,l) = (0.60)YbF2(g) + (0.40)YbF3(g), Reaction (a); and YbF3.00(s,l) = (0.05)YbF2.40(s,l) + (0.95)YbF3(g) + (0.03) F (g), Reaction (b). % A target collection Knudsen effusion method was used to determine vapor pressures for the above reactions. From the slope–intercept data the following enthalpy and entropy changes with associated standard deviations were derived at the median temperatures: For Reaction (a), ΔH°1597 = (96.9±1.1) kcal mol−1 and ΔS°1597 = (36.83±0.67 %cal mol−1⋅K−1; for Reaction (b), ΔH°1568 = (91.19±0.41) kcal mol−1 and ΔS°1568 = (37.28±0.26) cal mole−1⋅K−1. Estimated and reported thermodynamic functions were employed to reduce the thermodynamic values to 298 K. The reduced values are as follows: For reaction (a), ΔH°298 = (110.7±2.3) kcal mol−1 and ΔS°298 = (50.8±2.2) cal mol−1⋅K−1; for Reaction (b), ΔH°298 = (111.1±1.3) kcal mol−1 and ΔS°298 = (56.2±1.5) cal mol−1⋅K−1. By use of the third‐law procedure, the following ΔH°298 values were derived: for (a), (109.8±2.4) kcal mol−1; for (b), (107.0±3.0) kcal mol−1. The enthalpies and entropies for the hypothetical congruent sublimation reactions of YbF2(s) and YbF3(s) are derived and compared with those of the alkaline earth difluorides and other selected lanthanide fluoride systems.

Strained−layer superlattices form a broad new class of semiconductor materials with tailorable electronic properties. We have succeeded in growing a GaAsxP1−x/GaP(100) strained−layer superlattice (SLS). The structure was grown by alternate metalorganic chemical vapor deposition of thin (60 A)layers (20 each) of GaAs0.4P0.6 and GaP. These layers were grown onto a GaAsxP1−x layer which was graded in composition from x = 0 (composition of underlying GaP substrate)to x = 0 (average composition of the SLS). Photoluminescense studies of the SLS were carried out to determine the optical band gap. At T = 78 K, the spectrum shows a dominant band−edge peak at 2.03 eV as well as weaker peaks at higher energies. Tight binding and effective mass calculations, also carried out, predict a direct band gap (due to zone folding) of 2.02 eV and higher lying transition energies which are in good agreement with these data.

Both large photoconductive gain and long wavelength photoresponse were observed in lateral photodetectors constructed from type II, InAsSb, strained‐layer superlattices. In a novel, four‐layer superlattice, gain values as large as 90 are reported with a long wavelength cutoff of 8.7 μm at 77 K. The gain is sensitive to the structure and composition of the superlattice, and the sweepout of minority carriers is eliminated with the appropriate contacts.

We have made the first measurements of the minority‐carrier diffusion lengths L∥ and L⊥ respectively in both n‐ and p‐ type GaP/GaAsxP1−x 〈100〉 strained‐layer superlattices (SLS’s) in directions parallel and perpendicular to the interfaces. Using room‐temperature optical techniques, we find that L⊥≊0.1 μm, which is more than an order of magnitude smaller than L∥≊1.5 μm. The latter is comparable to that measured in the bulk materials which comprise the SLS layers, while the former demonstrates the existence of large potential barriers in both the conduction and valence bands.

Deep level transient spectroscopy measurements have been performed on pn jucntions in a strained‐layer superlattice (SLS) wafer composed of 240‐A‐thick alternating layers of GaP and GaAs0.3P0.7 grown by metalorganic chemical vapor deposition. Comparison of these results with data taken on a standard alloy buffer layer of nearly the same average composition (18% As) reveals that in the SLS there are fewer types of traps, the trap concentrations are usually lower, the sample to sample variations across the wafer are much less, and the trap depth profiles are more uniform. Consequently, this comparison suggests that the SLS material is of better quality than the buffer which is mismatched to the underlying GaP substrate.

The microscopic optical quality of thick (∼1 μm) III‐V semiconductor epitaxial layers, mismatched to their substrates, is examined by photoluminescence microimaging. The layers include several kinds of strained‐layer superlattices (GaP/GaAsxP1−x, GaAs/GaAs1−xPx, and GaAs/InxGa1−xAs) and associated alloys. Microscopic images of epilayer luminescence directly reveal the presence of misfit dislocations which appear as dark line defects. These defects can be completely eliminated in the strained‐layer superlattices if these structures have thin layers, less than the critical thickness for elastic accommodation, and sufficient numbers of interfaces of block threading dislocations.

Infrared photoluminescence measurements were performed on InAs0.13Sb0.87 /InSb strained‐layer superlattices. In thick layered structures we observed very low energy transitions proving that a type II superlattice occurs in the InAsSb system. Band structures were calculated based on estimates of the band offsets and strain shifts obtained from the photoluminescence data.

We present Hall‐effect measurements of the first localized p‐type doping in GaAsxP1−x /GaP strained‐layer superlattices achieved by implantation of 1×1015 cm−2, 75 kV 9Be+ followed by controlled‐atmosphere annealing at 825 °C for 10 min. The acceptor activation (∼15% at 300 K) and the mobilities in the p regions (∼20 cm2/Vs at 300 K) are consistent with the values expected for type‐converted GaP‐based alloys. Depth‐dependent structural characterization by ion channeling demonstrates that the superlattice structure survived the implantation and annealing without loss of layer strain. These results demonstrate that Be implantation can be applied to produce localized doping in a strained‐layer superlattice system and reflect favorably on the stability of strained‐layer superlattices under particle bombardment and thermal cycling.

We demonstrate the first direct measurement of strain in InxGa1−xAs/GaAs strained‐layer superlattices by ion channeling angular scans. This technique permits quantitative measurement of the strain without requiring computer simulations of dechanneling. The measurements are generally applicable to the study of strain in heteroepitaxial layers.

The capability of independently varying band gaps and lattice constants in ternary strained‐layer superlattices has been experimentally demonstrated for the first time. High‐quality GaAsxP1−x/GaP superlattices (0

We report, for the first time, temperature‐dependent Hall data for holes in modulation‐doped In0.2Ga0.8As/GaAs strained‐layer superlattices. Samples with (compressive) planar strains of −0.5% to −1.2% in the InGaAs quantum wells were used, providing a range of configurations for the two (overlapping) sets of valence‐band quantum wells derived from the bulk heavy‐ and light‐hole bands. All samples exhibit transfer of holes into the InGaAs quantum wells at low temperature; however, the sample with the least strain shows evidence for gradual carrier freeze‐out over a wide range of temperature.

We demonstrate the first Be+‐implanted lateral In0.2Ga0.8As/GaAs strained‐layer superlattice (SLS) avalanche photodetector. This planar device exhibits low capacitance (

Using metalorganic chemical vapor deposition, we have produced single‐crystal optical interference filters (high reflectors and antireflectors) with alternating quarter‐wave thick layers (in the range 300–600 A) of GaP and GaAsxP1−x. We have measured reflectance values from 0.08 to 0.90 at selected wavelengths from 460 to 750 nm. These filters have the unique feature that their design wavelength can be shorter than that corresponding to the energy band gap of the multilayer. In addition, we have produced an integrated optical detector in which a photodiode and an electrically active high reflector were grown sequentially in a single growth run. The spectral characteristics of the filters and integrated detector are reported here.

We have characterized damage production in both (InGa)As/GaAs and Ga(AsP)/GaP strained‐layer superlattices (SLS’s) for fluences sufficient to induce compositional disordering at three different implant temperatures. Dramatically different implant temperatures are required to produce similar defect distributions between the two SLS systems. Implants at lower temperatures [80 K for the (InGa)As/GaAs system, 300 K and below for the Ga(AsP)/GaP system] exhibit amorphous zones at depths consistent with the predictions of ion range codes; while implants at elevated temperatures [25 °C in (InGa)As/GaAs, 400 °C in the Ga(AsP)/GaP system] exhibit greatly reduced damage levels characterized mainly by extended defects.

Strained‐layer superlattices of InAsSb were grown with low densities of dislocations and microcracks for optical characterization to determine the suitability of these structures for infrared photodetectors. Infrared transmission measurements revealed absorption throughout the 8–12 μm region and extended to longer wavelengths than predicted from consideration of the tensile strain‐induced band‐gap shift in a type‐I superlattice. We conclude that a type‐II superlattice occurs in the InAsSb system for alloy compositions >60% Sb.

Virtually total suppression of carrier‐driven photochemical etching of semi‐insulating GaAs, n‐GaAs, and n+‐GaAs has been achieved by indiffusion of Zn to a surface carrier concentration greater than 1020/cm3. This technique for photochemical reaction suppression can be used as a self‐aligned etching technology for semiconductor device fabrication.