Silicon growth by Molecular Beam Epitaxy has great advantages for device fabrication. It can readily provide doping profiles with arbitrary and complex shapes, in any sequence, with abrupt transitions without smearing or compensation. Excellent depth and doping control results for layer thickness down to a few angstroms. Examples are shown of profiles that have already been grown for varactor diodes, avalanche and tunnel diodes, a low barrier Schottky diode and an n-p-n bipolar transistor.

AlxGa1-xAs/GaAs multiple quantum well (MQW) heterojunction structures have been grown by molecular beam epitaxy. Photopumped structures having quantum well sizes as low as 28 Å have shown 300 K and cw performance. MQW's with 28 Å well sizes grown at a substrate temperature of 720°C resulted in an equivalent current density of 2.3 kA/cm2 at a wavelength of about 7,270 Å.

For both space and terrestrial applications, improvement of solar cell conversion efficiency has a strong leverage on the power/weight and power/cost ratios for photovoltaic arrays. Currently, several strategies for efficiency improvement are being actively pursued. These include (1) the use of sunlight concentration which, in addition to improving specific cell efficiency, also substitutes relatively sheap concentrator cell area for relatively expensive cell area, (2) the use of direct bandgap semiconductors which absorb all the usable photons in only a few microns of material and also can provide a better match to the solar spectrum, and (3) the assembly of carefully chosen combinations of differing band-gap semiconductors into multijunction cascade convertersl. The latter multijunction cascade strategy provides a particularly potent means of improving the overall converter efficiency.

An AsCl3 vapor phase epitaxial reactor has been constructed which is capable of operation with a variable controlled Ga/As ratio. Layers grown in this reactor have been characterized by photoluminescence, electrical and DLTS measurements. Results to date indicate differing influence of the Ga/As gas phase ratio on <100> and <211A> orientation layers, particularly on deep level incorporation.

Over the past decade indium phosphide has become one of the most intensively studied semiconducting materials. A high saturation velocity and large peak to valley ratio in its velocity field characteristic make it an attractive alternative for many high performance microwave electrical devices. Interest in the InP-InGaAsP alloy system has been further stimulated by the need for emitters and detectors in the 1.3 to 1.55 μm region where the performance of low loss silica fibers is optimal. In addition, an energy gap which is nearly ideal for conversion of solar radiation to electrical power makes it an interesting compound from that point of view. The ability to grow high purity epitaxial layers is important for the evaluation of fundamental material parameters and for controlling the doping level to optimize the performance of specific devices.

This paper describes a method for the reproducible Si-doping of GaAs epitaxial material in the range of lx1016 to 2x1019 cm-3, using a SiCl4 + AsC13 liquid source in a GaAs + Ga/H2/AsC13 chemical vapor deposition process. Excellent electron mobilities have been achieved for a variety of Si doped GaAs samples. Power FET devices made from this material have demonstrated output power densities of 0.86 watts/mm at 10 GHz. Low noise FET devices made from this material have demonstrated a noise figure of 2.2 dB with 8.5 dB associated gain at 12 GHz.

Vapor phase epitaxial growth, using a PC13-In-H2 system, has been used to produce InP Gunn devices for the millimeter wave range. Several different multilayer profile configurations have been utilized to produce state-of-the-art performance in the areas of low noise amplifiers, medium power amplifiers and high efficiency Gunn oscillators for operation throughout the 26-140 GHz range. Typical doping profiles of each device structure, as well as the growth procedures required for each profile, are discussed. Device fabrication techniques and measured rf data are also presented.

The chemical vapor deposition of indium phosphide using the In/HCl/PH3/H2 reactant system is described. The deposition kinetics were studied as function of reactant concentration and substrate temperature. Studies of deposition of both polycrystalline and single crystalline material indicated that the growth rate of the thin films was limited by surface kinetics via a Langmuir-type absorption mechanism. Stoichiometry of the gas phase influenced the electrical properties of the as-grown epitaxial layers. For a group V/III ratio of 0.70 in the growth ambient, net donor densities of 1.5 x 1016 cm-3 were observed in the undoped epitaxial layers. Transient capacitance spectroscopy indicated deep level concentrations of the order 1-10 x 1014 cm-3 in the n and p-type epitaxial InP.

Laser spectroscopy techniques have been demonstrated for monitoring of gas-phase reactants in a system designed to simulate a hydride transport vapor phase epitaxy (VPE) reactor used to grow InxGa1-xAsyP1-y. Using a single excitation wavelength, unique emissions characteristic of InCl,GaC1, P2, As2, As4, PH3, and AsH3 can be resolved under typical VPE conditions (700°-800°C, 1 atm total pressure) making this technique ideally suited for nonintrusive, real-time, simultaneous monitoring of these species during growth. Detection limits range from 10-5 to 10-8 atm, well below species concentrations typically expected under growth conditions (10-3 -10-4 atm). The details of this technique and some examples of its use in determining VPE growth conditions are presented.

The OMVPE growth technique has only recently been established to yield device quality III-V compounds and alloys. The alloy receiving the most attention has been AlxGa1-xAs because of its application to lattice matched heterostructure devices such as solar cells and lasers, including multiquantum-well structures. This paper briefly reviews the development of OMVPE for the growth of AlxGa1-xAs, including a discussion of problems which were solved to reach the current state-of-the-art. The fundamental aspects of OMVPE growth are discussed, especially emphasizing fundamental advantages and disadvantages of OMVPE relative to other growth techniques such as LPE, MBE, and halide VPE. Other less fundamental aspects of OMVPE relating to purity, uniformity, surface morphology, and flexibility are also discussed. The current status of OMVPE AlxGa1-xAs material and devices is summarized.

Vapor-phase epitaxy (VPE) systems for the growth of 1) GaAs on Cr-doped GaAs substrates, and 2) lattice matched GaInAs and GaInAsP on Fe-doped InP substrates are briefly described. Layer composition of the ternary and quaternary compounds were measured by electron probe microanalysis, lattice mismatch by X-ray diffractometry, average carrier concentration and mobility determined using the Van der Pauw technique. Carrier profiles were investigated using an electro-chemical profiler. Several hundred n-type Ga0.47In0.53As/InP structures have been grown and characterized. Unintentionally-doped layers with a carrier concentration of 2x1015cm-3 and μ(300) and μ(77) of 11x103 and 38x103cm2V-ls-1, respectively, were realized. These represent the highest mobility values reported for VPE Ga0.47In0.53As at this doping level. Se-doped n-layers ranging in thickness from 0.2 to several μm and with carrier density from 1x1016 cm to 3x1018cm-3 + were grown. n-n structures with sharp n+-n transitions were grown for device fabrication studies. The doping profile of a 2 cm x 1 cm ternary layer grown using a rotating substrate holder was found to be fairly uniform; this n+-n wafer had an n+-layer doping of 1.6±0.1x1018cm-3, n+-layer thickness of 0.31±0.01 μm, n-layer doping of 9.5±0.5x101bcm-3, and n-layer thickness of 0.3±0.03 μm. The mobility profile of submicrometer n-layers was measured using the differential Van der Pauw technique. The high mobility was found to be maintained down to the ternary-substrate interface.

It is shown that the steady state chloride growth process is thermodynamically similar to the hydride growth process. The observed growth rate dependence on the input PC13 pressure at lower PC13 pressures and on the downstream PC13 pressure can be explained for the chloride system using thermodynamics. The shape of the growth rate curves as functions of the input HCl and PH3 pressures can be described thermodynamically at lower pressures. The background carrier concentration in chloride grown films as a function of the input PC13 concentration can be explained thermodynamically, but the effects of downstream PCl3 cannot.

Fourteen years have elapsed since our laboratory first reported the successful use of metalorganic-hydride combinations for producing epitaxial compound semiconductor films and alloys on insulating substrates and semiconductors. The technique has since been applied to the formation of a variety of III-V, II-VI, and IV-VI semiconductor compounds and alloys. More recently II-IV-V2 compounds were also produced. Successes in our laboratory and others and the application of the technique to devices continue to point to the process as the most viable one available today to produce large area growth of many types of films. Since much of the early work was performed in our laboratory, it may be of interest to this audience to become familiar with the steps that had to be climbed and the problems that were met in attaining the degree of quality now available in films grown by metal organic chemical vapor deposition (MO-CVD).

Stripe geometry lasers grown by MO-CVD lasing at 8260 Å (-7% Al in the active region) were characterized. Pulsed current thresholds vary little with stripe width for 4, 6, and 8 microns. The lowest pulsed threshold was 31 mA for a 125-µm-long device. This laser with a 6 μm stripe exhibited a kink-free light output vs. current characteristic up to 15 mW/facet and had a differential quantum efficiency nD ≈ 76%. The threshold currents and the increase of laser threshold with increasing cavity length were found to be significantly lower than those of previously-published devices. For 51 lasers that are 200±10 μm long with 4, 6, or 8 μm stripe widths, the average threshold currents were 40.4 mA, 41.1 mA, and 42 mA, respectively, and 37 of these lasers fall within ±1 mA of these averages. External differential quantum efficiencies for these same lasers are 75%, 67%, and 63%, respectively.

Atmospheric and low pressure (76 torr) epitaxial growth of gallium arsenide (GaAs) from trimethyl gallium (TMG) and triethyl gallium (TEG) has been studied. The results indicate that both TMG and TEG are capable of yielding high purity GaAs epitaxial layers. TMG is the preferred compound when large area uniform layers are desired at all reactor pressures. TEG is recommended only in those cases where carbon acceptor free GaAs is required and low pressure capability is available.

Monolithic multicolor solar cells offer the potential of very high energy conversion efficiencies for concentrated sunlight systems. The development of these cells will require the sequential fabrication of low and high band gap junctions in a continuous process system. This paper describes the fabrication of GaAs (0.82)P(0.18) solar cells via vacuum metalorganic chemical vapor deposition (MO-CVD) and their evaluation. GaAs (0.82)P(0.18) junctions can be used for the high band gap junction in multicolor cells, and the vacuum MO-CVD system is a potential continuous process system for these cells. Shallow homojunction GaAs (0.82)P(0.18) cells with active area efficiencies of 14.8% at 7.4 suns are obtained despite a 0.8% lattice mismatch between the cell active layers and the GaAs substrate.

The use of the column V trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs1-ySby, Al x Ga1-xSb and Ga1-xInxAs as examples.

Electrical properties and the impurity energy levels in Se-doped n-Ga(l-x)AlxAs (0≤x≤0.82) and Zn-doped p-Ga1-xAlxAs (0≤x≤1) prepared by metalorganic chemical vapor deposition have been investigated. The van der Pauw technique was used to measure the electrical properties of Ga(l-x)AlxAs. The resistivity and carrier concentrations of Ga(1-x)AlxAs were found to be strongly affected by the impurity energy levels for Se and Zn. Tne donor energy levels, ED, of Se in Ga(1-x)A1xAs was found to take the form of an inverted V with a maximum at the direct-indirect band crossover while the acceptor energy levels, EA, of Zn was found to increase with increasing A1 mole fraction.

The electrical properties of unintentionally-doped InP epitaxial layers grown on (100) InP:Fe substrates by Metalorganic Chemical Vapor Deposition (MOCVD) have been studied as a function of the source materials and the deposition conditions. The low-temperature (77K) photoluminescence of these films was also studied and used to identify zinc as the major residual acceptor in these films.

Liquid phase epitaxy (LPE) is a method of crystal growth well suited to the preparation of a wide range of compound semiconductor materials including GaAs, AlAs, GaP, InP, and GaSb, as well as their ternary and quaternary alloys. The advantages of LPE over other solution growth methods are substantial, primarily in material purity, doping flexibility, and dimensional control. It has particular advantages in achieving the complex multilayer structures required for many interesting optical devices, such as injection lasers, light emitting diodes, and photodetectors. LPE has appeared in many configurations in recent years, with the dominant variation at present being the sliding boat method. A good understanding of the capabilities of this method can be obtained by studying the growth of GaAs-AlxGa1-xAs heterostructures.

The morphologies observed on layers of III-V compounds and their alloys grown by Liquid Phase Epitaxy (LPE) are reviewed; these include: facets, terraces and the effect of small misorientation of the substrate; effects due to both the moving and the static three-phase boundary line on the surface of the crystal; nucleation effects; and the effects of insoluble particles in they solutions.

Near ideal injection lasers can be grown by liquid phase epitaxy but the growth process must include etching of a first epitaxial growth and controlled wetting, melt back and re-growth in a second growth cycle. The growth and properties of two such lasers, the strip buried heterostructure (SBH) and loss stabilized buried optical guide (LSBOG) are described in some detail. Similar growth procedures provide integration of lasers with waveguides, modulators, distributed Bragg reflectors and the formation of uniform arrays of lasers with laser to laser separation as close as 15 μm.

The control of thickness uniformity and compositional homogeneity is extremely important in the growth of high quality heterostructure lasers. This is especially important in the growth of the thin active layer of these devices. Slider induced convection within the growth solution in the horizontal LPE system can affect both of these factors and has been largely neglected in the modeling of layer growth. A Plexiglas boat with water and dyes was used to simulate the fluid motions in the melts of the horizontal LPE system. The simulation shows that there are substantial fluid motions induced by the movement of the slider. The duration of the convective cell thus generated can be comparable to the growth time of thin layers. Therefore, a substantial portion of the growth time for thin layers is under nonsteady state conditions where the solution is not static. Furthermore, convection dominates in the initial period of epitaxial growth. The dependence of the convective cell on melt geometry is discussed. A video tape was made showing the solution dynamics of several boat designs used in the growth of (GaA1)As heterostructure lasers.

Single layers of Ga1-xAlxAs were grown on semi-insulating Cr-doped GaAs substrates by liquid phase epitaxy. The samples consisted of six series. Within each series, the mole fraction of Al ranged from 0 to 0.45. Each series was either doped p with Ge or n with Te. The doping levels ranged from 1015 to 1019 carriers/cm3. The mole fraction of Al in each sample was measured independently by Auger electron spectroscopy, ion microprobe mass analysis, and photoluminescence for comparison with phase diagram predictions. The carrier concentrations were estimated by the half-width of the photoluminescence peaks. The techniques, their discrepancies, and agreements are discussed.