AlxGa1-xas Growth by OMVPE Using Trimethylamine Alane

High quality AlxGa1−xAs has been grown by low-pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) using a novel precursor, trimethylamine alane (TMAAl), as the aluminum source. The epilayers exhibited featureless surface morphology, very strong room-temperature photoluminescence (PL), and excellent compositional uniformity (x=0.235±0.002 over a 40 mm diameter). The residual carbon incorporation, which determined the background doping, depended largely upon the choice of gallium precursor. Using triethylgallium, carbon incorporation could be largely suppressed ([C]≪1016 cm−3). The carbon-related emission intensity was less than the bound exciton emission in low-temperature (1.6 K) PL even at excitation powers as low as 50 μW cm−2. By sharp contrast, the use of trimethylgallium led to much higher C concentrations (2–5×1017cm−3). Under appropriate conditions, therefore, the use of TMAAl produces extremely high purity AlGaAs of superior quality to AlGaAs grown using conventional precursors.

We have investigated the effects of gas phase reactions between trimethylamine alane (TMAA), triethylgallium (TEG), and arsine on AlxGa1−xAs films grown by low pressure organometallic vapor phase epitaxy. The reactor used in this study provides for independent observation of the effects of TEG-TMAA and TMAA-arsine gas phase reactions. Gas phase reactions involving TMAA and TEG result in the formation of nonvolatile compounds upstream, which condense on the reactor wall, resulting in a reduction of growth rate and a degradation of the deposition uniformity. The TMAA-arsine reaction produces a compositional dependence on the gas phase stoichiometry (V/III ratio). Both of these effects are more severe for higher TMAA fluxes. High quality AlGaAs with excellent thickness and compositional uniformity was produced by spatially separating the TMAA and TEG in the gas phase which minimizes the parasitic reactions.

The carbon doping properties of GaAs grown by low pressure (30 Torr) organometallic vapor phase epitaxy at 520–700 °C with CCl4 as the dopant precursor were compared for the four possible combinations of trimethylgallium (TMGa), triethylgallium (TEGa), arsine (AsH3), and tertiarybutylarsine (TBAs). Secondary ion mass spectrometry (SIMS), Hall measurements, and infrared absorption were used to characterize the GaAs:C layers. Very high C-doping concentrations (∼1020 cm−3) could be obtained using either TMGa or TEGa and AsH3. The use of TBAs instead of AsH3 led to a significant reduction in carbon incorporation, by approximately a factor of 5–10 per mole of As precursor over the growth temperature range examined. Hydrogen at significant concentrations (1–6×1019 cm−3) was detected by SIMS in GaAs: C layers grown at ≤550 °C utilizing all four combinations of Ga/As precursors. The existence of electrically inactive C-H complexes was confirmed by observation of the C-H stretching mode at 2635 cm−1. A post-growth anneal under helium at 550 °C for 60 s removed the C-H pairs resulting in a 50%–100% increase in hole concentration. There was no change in the hole concentration for GaAs:C grown at ≥600 °C, indicating negligible hydrogen passivation.

Two different kinds of n-type GaN films were prepared by organometallic vapor phase epitaxy, one by using trimethylgallium (TMGa) and another by using triethylgallium (TEGa) as the alkyl source. Schottky diodes with well-behaved current–voltage and capacitance–voltage characteristics were fabricated. Deep-level transient spectroscopy studies were performed on these samples. Three distinct deep levels, labeled E1, E2, and E3, were measured in the film grown with TMGa, with an activation energy of 0.14, 0.49, and 1.63±0.3 eV, respectively. Only one level, E3, was observed in the film prepared with TEGa.

GaAs buried growth over tungsten stripe using TEG and TMG

(AlxGa1−x)0.51In0.49P layers, lattice matched to (001)-oriented GaAs substrates, have been grown throughout the entire aluminum composition range from x=0 to 1.0 by atmospheric pressure organometallic vapor-phase epitaxy (OMVPE), using trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMln), and phosphine (PH3) as source materials in a horizontal reactor. The growth temperature was held constant at 680 °C. Excellent surface morphologies were obtained over the entire composition range. Unlike previously reported results, neither high growth temperatures nor low pressures were needed in order to obtain good-quality, high-x (AlxGa1−x)0.51In0.49P alloys using trimethylalkyls. Photoluminescence (PL) was observed, even at 300 K, for all samples with Al solid compositions of x≤0.52. The results show that the energy band gap measured by PL at room temperature for this material varies as Eg=1.9 +0.6x, in accord with previous studies. It was found that the PL emission intensity was nearly constant at 10 K with increasing x in the range from 0 to 0.52. This contrasts with earlier published results which showed a decreasing PL intensity for the higher values of x. The 300-K PL intensity was almost a constant for x≤0.3 and gradually decreased with increasing Al content for x>0.30. The dependence is nearly that predicted from a simple calculation based on the relative occupancies of the Γ and X conduction bands using a constant minority-carrier lifetime. The PL full width at half maximum (FWHM) for x=0 was 7.2 meV at 10 K and 35 meV at 300 K. These are the narrowest reported results to date. For x=0.48, the FWHM was 31 meV at 10 K and 78 meV at 300 K. It was observed that at both 10 and 300 K, the FWHM increased slowly with increasing aluminum concentration.

We have utilized a new aluminum source, trimethylamine alane (TMAA), in the growth of graded-index separate-confinement heterostructure single quantum-well GaAs/AlGaAs laser structures by low pressure (30 Torr) organometallic vapor-phase epitaxy. We find lower carbon and oxygen incorporation in AlGaAs epilayers using TMAA since it does not contain a direct Al–C bond and it is not susceptible to the formation of volatile Al–O containing compounds. The oxygen and carbon concentrations were below the detection limits (< 5 × 1016 cm−3 and < 3 × 1016 cm−3, respectively) of the secondary ion mass spectrometry measurements. Broad-area lasers with 10-nm quantum wells and Al0.45Ga0.55As cladding layers exhibited threshold current densities of 140 A cm−2 for cavity lengths of 1 mm, internal quantum efficiencies of 81%, and intrinsic losses of 1.6 cm−1. These results demonstrate that extremely high-quality AlGaAs and GaAs quantum wells can be grown with TMAA.

The authors have investigated the role of various arsenic precursors on the selectivity of GaAs and AlGaAs at low deposition temperatures, <or=525 degrees C, during growth by metal organic molecular beam epitaxy (MOMBE). The As2 generated from the cracking of AsH3 was found to induce nucleation on the SiN mask surface for both triethylgallium (TEG) and trimethylamine alane (TMAA). Trisdimethylaminoarsenic (DMAAs) produces identical behavior, probably due to its high decomposition efficiency, which also leaves free arsenic on the mask surface. By contrast, phenylarsine (PhAsH2) does not induce nucleation as readily due to its insufficient decomposition on the mask surface. Using PhAsh2, GaAs growth from TEG and AlGaAs growth from TMAA and trimethylgallium (TMG) were found to be highly selective. However, though selectivity was high, the surface morphology of the regrown area was typically rough due to contamination during processing. Various attempts at removing this contamination are also discussed.

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.

We present a comprehensive study on the growth of AlGaAs by using an alternative Al precursor, dimethylethylamine alane (DMEAA), and a Ga coprecursor, either triethylgallium (TEG) or trimethylgallium (TMG). The growth rate of AlAs determined by using in situ reflectometry was studied as a function of the growth temperature, V/III ratio, growth pressure, and rotation speed of the substrate. The presence of gas phase reactions of DMEAA with arsine and TEG was indicated, and their reduction was achieved at a lower growth pressure, lower V/III ratio, or a lower growth temperature. Negligible pre-reaction of DMEAA with TMG was observed. Excellent material uniformity of AlGaAs was achieved on a 2″ diameter wafer. Secondary ion mass spectroscopy measurements revealed extremely low C and O contents in the AlAs layer grown by DMEAA. Photoluminescence measurements suggested the presence of some non-radiative defects in the as-grown DMEAA AlGaAs layers.

We report the first low pressure (76 Torr) metalorganic chemical vapor deposition of AlxGa1−xN using trimethylamine alane (TMAAl) as the aluminum source. AlxGa1−xN epilayers deposited using TMAAl exhibited an excellent surface morphology and very strong room temperature photoluminescence. For AlN layers (using TMAAl as the aluminum precursor) we obtained a total carbon contamination level as low as 1017 cm−3.

High-quality GaAs/AlGaAs quantum well and modulation-doped heterostructures have been grown by low-pressure organometallic vapor phase epitaxy (OMVPE) using trimethylamine alane (TMAA) as a new aluminum source. TMAA is an alternative to the conventional organometallic precursors and offers the advantage of substantially reduced oxygen and carbon incorporation in AlGaAs. Intense photoluminescence (PL) with narrow linewidths at 2 K was observed from multiple quantum well samples with well widths of 1.5–10 nm. Transmission electron microscopy of a fifty period superlattice (4 nm GaAs/44 nm Al0.18Ga0.82As) revealed abrupt interfaces and excellent well-to-well thickness uniformity. Selectively doped heterostructure transistors (SDHTs) fabricated on the modulation-doped structures exhibited a maximum extrinsic transconductance of 339 mS/mm for a 1-μm-gate length at 300-K, the highest reported for OMVPE grown devices. A unity current gain cutoff frequency, ft, of 16 GHz and a maximum frequency of oscillation, fmax, of 23 GHz were obtained for these SDHTs.

Heavily doped p-type AlGaInP grown by metalorganic chemical vapor deposition

The transient capacitance method was used to analyze GaN samples grown by low-pressure organometallic vapor phase epitaxy (OMVPE) with triethylgallium (TEGa) or trimethylgallium (TMGa) as the alkyl source. Two deep levels at 1.10 and 1.27 eV were observed in the TMGa sample, while a deep level at 0.60 eV was observed in the TEGa sample. Using light illumination, levels deeper than those above were investigated in TEGa and TMGa samples.

Low temperature growth of AlGaAs by MOMBE (CBE) using trimethylamine alane