We have fabricated resonant tunneling diodes (RTD's) containing a GaInAs quantum well and strained GaInP barriers. These diodes exhibit good characteristics at 80 K with a peak to valley current ratio of 1.34 which is comparable to other reports for RTD in this material system. Additional RTD's were made using a InAs rich well region to study the effect of strain compensation. To investigate the properties of these structures, transmission electron microscopy (TEM) and low temperature photoluminescence (PL) were performed. TEM shows that both RTD structures contain misfit dislocations. PL measurements indicate that the dislocations are not significantly affecting the GaInAs quantum well.

A new application of selective area metalorganic vapour phase epitaxy is demonstrated: fabrication of distributed feedback (DFB) gratings with sub-micron period and modulated coupling coefficient Kc. A SiO2 mask layer defines the InGaAs(P) grating pattern as well as the lateral variation in growth rate and, hence, thickness of the grating. In this way K can be varied along the laser cavity in a controlled and reproducible manner.

Due to the extreme toxicity, and in the case of Sb stability, of the Group V hydrides, alternative gaseous Group V sources for III-V epitaxy are highly desirable. Trisdimethylaminoarsenic (DMAAs) has proven to be a useful replacement for AsH 3 for growth of GaAs and AlGaAs by MOMBE. This paper will discuss the P and Sb analogs to this compound, namely trisdimethylaminophosphorus (DMAP) and trisdimethylaminoantimony (DMASb). Both sources decompose readily on the growth surface. InP surfaces, for example, can be maintained with either source over a wide range, 375° - 525°C, as can GaAs, 375° - 600°C. Using DMAP, GaP can be grown at rates up to 200Å/min with slightly less carbon contamination than obtained with similar flows of PH3. When trimethylindium (TMI) is introduced, however, the DMAP does not readily decompose thus leaving In droplets on the surface. InP was successfully grown by thermally cracking the DMAP prior to injection to the chamber. The dependence of cracking efficiency and impurity uptake on cracker temperature will also be presented. DMASb was found to produce just the opposite effect, apparently preventing the adsorption of TEG, TIBG, or TMAA on the surface for sufficient time to allow growth to occur.

Phosphorus (P)-based alloys are important for applications in areas including optoelectronics and high speed electronics. Gas phase technologies such as organometallic vapor phase epitaxy (OMVPE) and chemical beam epitaxy (CBE) have traditionally used the extremely dangerous hydride, phosphine (PH3). Less hazardous alternatives need to be found. Three such alternative P-sources are: tertiarybutylphosphine (TBP), bisphosphinoethane (BPE) and trisdimethylaminophosphine (TDMAP). InP and GaP growth results using TBP, BPE, and TDMAP along with a brief discussion of the pyrolysis of these alternative P-sources are presented. InP has been grown using ethyldimethylindium and pre-cracked BPE with excellent surface morphology and strong 10 K photoluminescence with a half width of 4.8 meV. The residual doping level typically was in the high 1015 to low 1016 cm-3 range. GaP has been grown at a substrate temperature of 480°C without precracking the TDMAP.

In this paper, we report chemical beam epitaxy (CBE) of GaAs, and for the first time, Arion laser-assisted CBE using triethylgallium (TEGa) and tris-dimethylaminoarsenic (TDMAAs), a safer alternative to arsine. Samples grown at substrate temperatures above 490° C show n-type conduction, while those grown at lower temperatures show p-type conduction. An unintentional doping concentration of n∼lx1016 cm-3 with an electron mobility of 5200 cm2/V.s at 300 K and 16000 cm2/V.s at 77 K have been achieved. These are the best results reported for GaAs grown with TDMAAs. Laser-assisted CBE of GaAs is studied in the substrate temperature range of 240-550°C. There are two different substrate-temperature regions for laser-enhanced growth, 265 to 340°C and 340 to 440°C, which are believed to be caused by different TEGa decomposition mechanisms. The laser-assisted growth with TDMAAs, compared to AS4 or AsH3, shows a wider range of growth enhancement at low substrate temperatures.

Low levels of arsenic contamination have been previously reported (∼0.01%) in CBE grown InP by different groups. The level of As incorporation in InP is usually enhanced when arsenide(InGaAs, InAsP) / InP heterostructures are grown.

In this work, optimal growth conditions to minimize the non-intentional As contamination during the growth of these heterostructures are discussed. The red shift of band-edge excitons in the low temperature photoluminescence spectra as well as the analysis of high resolution X-ray diffraction patterns of InAsP/InP multi-quantum wells suggest the presence of As in InP barriers. This contamination is consistent with the ratio of As/P partial pressure (As residual in the chamber: 10-9-10-8 Torr) and the As/P incorporation rates. We have studied the influence of the growth temperature, the group-V/III flux ratio and the growth rate on the level of the As incorporation.

A comparison of dimethylethylamine alane (DMEAA) and trimethylamine alane (TMAA) as aluminum sources and CBr4 and CC14 as carbon doping sources for deposition of AlAs by metalorganic molecular beam epitaxy (MOMBE) has been carried out. DMEAA was found to produce the lowest oxygen levels in AlAs, 5 x 1017 cm-3 VS. 1021 cm-3 for TMAA, even at growth temperatures as low as 500°C. This reduction is likely due to the absence of oxygenated solvents used during synthesis of the DMEAA. Undoped films grown from either source were fully depleted as-grown. Through the use of CBr 4, hole concentrations up to 4.5x1019 cm-3 were achieved in AlAs layers grown fiom DMEAA. Attempts to increase the hole concentration beyond this level resulted in a decrease in the hole concentration even though SIMS analysis showed the carbon concentration to increase with increasing dopant flow. Though the carbon sources did not appear to introduce additional oxygen, they appear to introduce other impurities, such as Cl and Br. Also, due to parasitic etching reactions with the adsorbed halogen, the use of these sources reduces the Al incorporation rate.

Metalorganic molecular beam epitaxy (MOMBE) of GaAs using triethylgallium (TEGa) and As4 has been studied by reflection high-energy electron diffraction (RHEED). The effect of varying the group-Ill flow rates and group-V beam flux on the growth rate has been investigated over a wide range of substrate temperatures. For a given arsenic flux, the GaAs growth rate first increases linearly as the TEGa flow rate increases. This linear relation extends up to a certain TEGa flow rate, where the growth rate reaches its maximum value. When the TEGa flow rate is increased above this critical value, the growth rate decreases and reaches a stabilized value. From a study of both group-Ill and group-V induced RHEED intensity oscillations, we find that the V/Ill incorporation ratio is unity at the transition point. Compared to conventional molecular beam epitaxy (MBE), MOMBE behaves differently when the V/Ill incorporation ratio is less than unity. The transition region between V/III>I and V/III<1 is gradual and no excess gallium accumulates on the surface during growth. The arseniccontrolled growth rate obtained from conventional group-V induced oscillations where excess Ga atoms are present is greater than the growth rate in the stabilization region where V/IIl<1.

Sulfide passivation of optically pumped GaAs/AlGaAs microdisks (at 77K) was examined. The microdisks had diameters between 2 and 10 µm and thicknesses of 0.2 µm. The layer structure was grown by organometallic vapor phase epitaxy. An ammonium sulfide solution was used for the passivation. The GaAs/AlGaAs microdisks without the sulfide treatment did not lase when optically pumped, even at the highest pump power densities of 10 kW/cm2. With sulfide treatment cw lasing was achieved with a lifetime of several seconds. A dramatic increase in the laser lifetime was obtained when the sulfide treated samples were encapsulated with silicon nitride in order to prevent loss of sulfur and surface oxidation. In addition to the lifetime increase, the laser output could be increased by nearly an order of magnitude by annealing at 400°C for 300 s or by cw operation over a period of hours at pumping powers near 10 kW/cm2.

We observed a second-harmonic generation (SHG) in reflection from a GaAs (100) surface during an oxide removal process using a pulsed hydrogen plasma. We found that the P-polarized SH intensity under P-polarized excitation decreased in the [011] azimuth of incidence and increased in the [011] azimuth of incidence during hydrogen plasma irradiation. The input polarization angle dependence of the P-polarized SH intensity before and after oxide removal was fitted to a model which includes both the surface and bulk SHG contributions. We estimated the thickness of the removed oxide based on the bulk SHG contribution change.

We report attaining (3x2) surface reconstruction with streaky reflection high energy electron diffraction (RHEED) patterns on Al0.4Ga0.6As after in-situ Cl2 chemical etch and ultra high vacuum (UHV) anneal. Secondary ion-mass spectrometry (SIMS) analysis at the regrown/etched Al0.4Ga0.6 As interface reveals impurities of O and C in the level of (5±1) × 1012 cm-2 and (3±1) × 1012 cm-2, respectively. These impurity levels are 10 times less than those of Al0.4Ga0.6 As after in-situ electron cyclotron resonance (ECR) plasma etch and UHV anneal without Cl2 chemical etch.

An investigation was performed of surface region etch-induced damage of GaAs magnetron reactive ion etched in CH4/H2/Ar gas mixtures for 10% and 20% Ar concentrations. Schottky barrier I-V measurements showed that changes in surface potential (ϕb) upon etching and subsequent annealing can be explained by a combination of H passivation effects and As removal from the surface region. Changes in Schottky barrier ideality factor (n) can be explained by the presence of etch-induced surface region defects such as donor-like As vacancies and deep level recombination centers, both of which are passivated by H. Schottky barrier C-V measurements indicated that H passivation extends about 0.3 μm below the surface. Rapid thermal annealing at 400°C for 30 s was effective in removing most of the H passivation effects.

Laser reflectometry has been shown to be a useful tool for etch depth measurements during etching of multiple layer structures. We have extended the use of laser reflectometry to accurately determine the etch rates of GaAs, Al0.4Ga0.6As and AlAs as a function of temperature and to verify layer thickness in-situ. By use of computer simulation we compare a theoretical model to actual data to determine layer thicknesses and accurate etch rates. We compare our data to previously published work for GaAs etching.

Atomic force and scanning tunneling microscopy studies have been performed on GaAs(001) films grown by molecular beam epitaxy. Multilayered mounds are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased, these features grow in all dimensions but the angle of inclination remains approximately constant at 1°. The mounding does not occur on surfaces grown in stepflow. We propose that the multi-layered features are due to an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.

Cross-sectional scanning tunneling microscopy and spectroscopy have been used to characterize InAs/Ga1-x InxSb strained-layer superlattices grown by molecular-beam epitaxy. Atomic-resolution constant-current images of the epitaxial layers reveal monolayer roughness at the superlattice interfaces. An asymmetry in electronic structure between interfaces in which InAs has been grown on Ga1-x InxSb and those in which Ga1-x InxSb has been grown on InAs has also been observed in these images. Close inspection of the images reveals increased growthdirection lattice spacings in the Ga1-x InxSb layers compared to the InAs layers, as well as even larger lattice spacings at the InAs/Ga1-x InxSb interfaces. The latter is consistent with the formation of primarily InSb-like interfaces. Current-voltage spectra obtained while tunneling into the superlattice layers are found to be strongly influenced by extended superlattice electronic states.

We have prepared InAsSb/InGaAs strained-layer superlattice (SLS) semiconductors by metal-organic chemical vapor deposition (MOCVD) using a variety of growth conditions. The presence of an InGaAsSb interface layer is indicated by the x-ray diffraction patterns. The optimized growth conditions involved the use of low pressure, short purge times between the growth of the layers, and no reactant flow during the purges. We used MOCVD to prepare an optically pumped, single heterostructure InAsSb/InGaAs SLS / InPSb laser which emitted at 3.9 μm with a maximum operating temperature of approximately 100 K.

The presence of two species of both cations and anions permits the construction of InAs/AlSb heterostructures with either AlAs- or InSb-like interfaces. InAs/AlSb superlattices with both types of interfaces were grown using migration-enhanced epitaxial techniques. The layer quality and control of interfacial composition were confirmed by x-ray diffraction, Raman spectroscopy, and photoluminescence measurements. We demonstrate that high-quality superlattices with both InSb- and AlAs-bonded interfaces can be achieved with appropriate growth temperatures.

In this study, we demonstrate the enhancement of n-In0.53Ga0.47A s Schottky barrier height by using a thin (300-1800 Å) p-InP surface layer. An increase in the barrier height of 0.46 eV, making the total barrier height 0.66 eV, was obtained in a Au/p-InP/n-InGaAs structure, resulting in a great reduction of leakage currents. Results of the electrical measurements are summarized in table 1. The barrier height of n- In0.53Ga0.47As was increased from 0.2 eV to 0.66 eV when a 1200-Å-thick p-InP surface layer was employed.

It is shown that in Au/InGaP and Au/InGaAlP Schottky diodes the Fermi level is pinned by metal-deposition-induced midgap states. Hydrogen plasma treatment of such diodes greatly improves the reverse currents. The measured Schottky barrier heights seem to correlate with the valence band offsets measured by DLTS on quantum well structures.

Doping of III-V semiconductors is an essential part of growth and processing technology for optoelectronic and high speed electronic devices. This review covers several recent developments in III-V doping including (i) the high-concentration regime for p-type dopants in InP and GaAs, (ii) the sensitivity of doping incorporation on the crystal orientation, (iii) compensation mechanisms in Si-doped GaAs, and (iv) p-type carbon doping in GaAs and AlxGa1-xAs.