Interface strain in organometallic vapor phase epitaxy grown InGaAs/InP superlattices

The spatial distribution of strain in organometallic vapor phase epitaxy grown InGaAs/InP superlattice structures has been studied by varying the thicknesses of the InGaAs well and the InP barrier layers and measuring the strain. High resolution x-ray diffraction rocking curves were used to measure the strain from angular separation between the zeroth-order superlattice peak and the substrate (004) peak. The results are consistent with a compressive strain resulting from arsenic carryover into the InP following InGaAs growth. The strain is not localized at the interfaces but extends into the InP barrier layer. The amount of arsenic carryover increases with the growth time of the InGaAs well.     

Interfacial layer in homoepitaxial InP grown by organometallic vapor phase epitaxy with TMIn and TBP

The effects of interfacial layers with high impurity concentration on the properties of homoepitaxial InP layers have been studied by far-infrared (FIR) magnetoabsorption, in addition to dc mobility, Hall effect, and photoluminescence (PL) measurements. The layers are grown by organometallic vapor phase epitaxy with trimethylindium and tertiarybutylphosphine. Impurity absorption as well as cyclotron resonance is observed in the FIR measurements. Variations in the intensity of the resonance signals and the mobilities obtained from the linewidths of the cyclotron resonance are interpreted by a double layer model, i.e. a bulk layer with an interfacial layer. Carrier concentrations, dc mobilities, and PL intensities of both bound excitons and free excitons are also explained by the model.     

Crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy

The complete crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy (LPOMVPE) is determined using a previously described semi-empirical model. A set of LPOMVPE growth rate polar diagrams is presented for reactor temperatures near 550°C as well as near 700°C. Also, the variation of the growth rate polar diagrams as a function of process variables is given. The experimental data utilized in the semiempirical model was attained using a typical horizontal reactor LPOMVPE system and typical LPOMVPE process parameters.     

Growth of GaBN ternary solutions by organometallic vapor phase epitaxy

Layers of Ga_1-xB_xN with compositions from x = 0 to x = 0.07 were grown by organometallic vapor phase epitaxy on sapphire substrates using trimethylgallium, triethylboron (TEB) and NH₃ as precursors. Growth was done in the temperature range from 450 to 1000°C. The presence of boron was detected by the shift in the (0002) peak position in x-ray diffraction, by x-ray photoelectron spectroscopy, secondary ion mass spectrometry measurements, and by the changes in the band gap as measured by optical transmission. It was found that for the studied range of compositions the band gap varied from 3.4 eV for x = 0 to 3.63 eVfor x = 0.05. At certain TEB concentrations in the gas phase, the growth rate decreased abruptly, most likely because of a growth poisoning by the onset of growth of a very slow growing B-rich phase. The threshold TEB concentration for this growth poisoning decreased with increasing growth temperature; and at 1000°C, less than 1% of B could be incorporated as a result. GaBN alloys with about 7% substitutional boron were also produced by implantation of 5 × 10¹⁶ cm⁻² B ions at 60 keV into GaN, as evidenced by the shift of the band edge emission in cathodoluminescence spectra from 3.4 eV for GaN to 3.85 eV for GaBN.     

Growth of high quality CdTe and ZnTe on Si substrates using organometallic vapor phase epitaxy

Epitaxial (100) CdTe and ZnTe layers with high crystalline quality have been grown on Si substrates by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). A thin Ge interfacial layer grown at low temperature was used as a buffer layer prior to ZnTe and CdTe growth. The layers were characterized by Nomarski optical microscopy and double crystal x-ray diffraction. Double crystal rocking curves with full width at half maximum of about 110 and 250 arc-sec have been obtained for a 7 μm thick ZnTe layer and a 4 μm thick CdTe layer, respectively. The results presented demonstrate a novel method ofin-situ Si cleaning step without a high temperature deoxidation process to grow high quality CdTe and ZnTe on Si in a single OMVPE reactor.     

Step structure of GaInAsSb grown by organometallic vapor phase epitaxy

The surface step structure of Ga_1−xIn_xAs_ySb_1−y grown by organometallic vapor phase epitaxy on GaSb substrates has been studied by atomic force microscopy. Epilayers were grown at 525°C and 575°C on (001) GaSb substrates misoriented 2° toward (101) or 6° toward (1 1)B. For Ga_0.88In_0.12As_0.1Sb_0.9 grown at 575°C, the surface exhibits step-bunching on both types of substrates. When the composition is increased to Ga_0.86In_0.14As_0.12Sb_0.88, the periodic step structure breaks down and the surface becomes irregular. The deterioration of the step structure is a consequence of phase separation at the surface of the metastable GaInAsSb epilayer, which leads to the formation of GaAs- and InSb-rich regions. The photoluminescence (PL) of such layers show significant broadening due to carrier recombination in the lower energy gap InSb-rich quaternary regions. On the other hand, the surface of GaInAsSb epilayers grown at a lower temperature of 525°C is vicinal with steps heights of one to two monolayers. The PL FWHM values are considerably smaller for these layers. This improvement in material quality is related to smaller adatom lifetimes at the lower growth temperature. The importance of surface kinetics as it influences the step structure and thermodynamically driven phase separation is discussed.     

Compositional non-uniformities in selective area growth of GaInAs on InP grown by OMVPE

Selective area epitaxial growth of Ga_0.47In_0.53As on InP substrates patterned with silicon nitride was done by low pressure organometallic vapor phase epitaxy. Good surface morphology and clean side walls of the epitaxial layers were obtained in most of the areas of selective GalnAs growth. However, both GaAs incorporation and InAs incorporation increased near the edges of the selective growth areas due to the extra flux of Gacontaining and In-containing species migrating on the surface of silicon nitride. The increase in InAs incorporation was found at a higher rate when the adjacent silicon nitride area was large, hence, cross-hatching appeared near the edges. A characteristic length of adjacent silicon nitride seemed to be connected with the enhanced InAs incorporation, which was about 40μm at 600°. The non-uniformities in composition appeared in all wafers grown in the temperature range between 570 and 650°.     

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH₃ atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.     

The contraction of lattice constant and the reduction of growth rate in p-InGaAs grown by organometallic vapor phase epitaxy

We have investigated the effect of diethylzinc (DEZn) on the lattice constant and the growth rate of InGaAs. Introducing DEZn for p-type doping induces the contraction of lattice constant and the reduction of growth rate compared to undoped InGaAs. Depletion of indium is responsible for these effects. These effects are reduced at lower growth temperatures or at lower growth pressures. From the observed effects of the growth temperatures and the growth pressures on the contraction of the lattice constant, it is concluded that depletion of indium occurs in the gas phase.     

Adjusting trimethylgallium injection time to explore atomic layer epitaxy of GaAs between 425 and 500°C by organometallic vapor phase epitaxy

In experiments employing a conventional low-pressure, rotating-disk organome-tallic vapor phase epitaxy reactor, GaAs epilayers have been grown at substrate temperatures ranging from 425 to 500°C by exposing the substrate alternately to trimethylgallium (TMG) and AsH₃.The GaAs growth rateR was approximately constant with TMG flow rate, but with increasing TMG injection timet, it increased to more than one monolayer per TMG/AsH₃ cycle without saturating. Although growth was not self-limiting, for one specific combination of temperature andt, a value of R = 1 monolayer/cycle could be achieved by usingt values decreasing from 10.8 s at 425°C to 0.9 s at 500°C in accordance with an Arrhenius relationship between 1/t and absolute temperature.     

Chlorine auto-doping by chloride vapor phase epitaxial growth of InP

Chlorine auto-doping phenomenon was found for the first time in InP epitaxial growth by using a PCl₃/InP/H₂ system. Chlorine atoms act as a donor in the epitaxial layer and the carrier concentration is dependent on the facet of InP substrate. The carrier concentration of the InP layer on ( 111)B facet was over 10³ times higher than that on (111)A substrate.     

Metalorganic vapor phase epitaxial growth,characterization and annealing experiments on InP doping superlattices

InP doping superlattices (DSLs) were grown by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) and their stability was examined by annealing at high temperatures. Diethylzinc (DEZ) and H₂S were used asp- andn-type doping sources, respectively. Photoluminescence (PL) measurements performed on as grown layers show a shift of the main emission peak with increasing excitation power in very good agreement with theoretical models. A comparison of the PL results between these structures and the annealed samples show that even at very high temperatures (up to 850° C) the tunability of the effective bandgap of the annealed superlattices is possible, although less pronounced than for the as grown layers. This is due to diffusion of the dopants, into adjacent layers and partial compensation of each other. Secondary ion mass spectrometry (SIMS) done on the as grown and annealed samples shows that only the Zn atoms diffuse. Diffusion coefficients obtained from the SIMS profiles give values in the range 1 × 10⁻¹⁴ <D < 9 × 10⁻¹⁴ cm²/s, still smaller than other published values estimated on layers, which did not suffer any treatment. This shows the high quality and stability of our layers even at high temperatures.     

Selective area epitaxy and growth over patterned substrates by chemical beam epitaxy

Selective area epitaxy and growth over patterned substrate using chemical beam epitaxy (CBE) were investigated. Truly selective area epitaxy with no deposition over the SiO/sub 2/ masks has been routinely obtained with excellent epilayer morphology. Uniform coverage was obtained for regrowth over etched mesas to form buried heterostructures. For growth over etch channels, very unique growth characteristics were obtained. Buried crescent stripes similar to those formed by liquid-phase epitaxy inside channels were also obtained by CBE. These growth characteristics demonstrated the unique of CBE for diode laser fabrication.<>     

Optoelectronic integrated receivers on InP substrates byorganometallic vapor phase epitaxy

The monolithic integrated ion of a p-i-n photodiode and a high-electron mobility transistor (HEMT) amplifier on an InP substrate by organometallic vapor-phase epitaxy is discussed. The receiver operated with up to 1.6 Gb/s nonreturn-to-zero optical signals. The responsivity was 1 kV/W and the minimum optical power at a bit error rate of 10^-9 was -24 dBm for 400 Mb/s nonreturn-to-zero optical signals     

Growth of GaInP/GaAsP short period superlattices by flow modulation organometallic vapor phase epitaxy

One disadvantage of the GalnP/GaAs system is the difficulty often encountered in synthesizing the quaternary material GalnAsP, required to span the intermediate bandgap range (1.42–1.91 eV). Recent studies report on an extensive miscibility gap in this alloy. In this study, we investigate an alternative approach to the growth of material within this bandgap range. We have grown by flow-modulation organometallic vapor phase epitaxy, GalnP/GaAsP superlattices with periods ranging from 80 to 21Å. These are the first reported short-period superlattices in this material system. Effects of superlattice (SL) period, growth temperature, and phosphorous composition in the wells were studied by photoluminescence, high resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The effect of growth temperature on the structural quality of the SLs is correlated to ordering effects in the GalnP layers. Variations in the P composition and the SL period result in a shift in the room temperature bandgap emission from 1.51 to 1.74 eV. Strain-compensated structures have been realized by growing the SL barriers in compression.     

The morphology of CdTe deposited by organometallic vapor phase epitaxy: The effect of substrate misorientation

Substrate misorientation and growth temperature influence the morphology of CdTe epilayers grown by organometallic vapor phase homoepitaxy. These effects were investigated by using CdTe{100} and CdTe{100} misoriented by 2, 4, 6, and 8° toward 〈111〉_Te as substrates for growth in the temperature range from 337 to 425°C. Low angle pyramidal facets appeared on films grown on the CdTe(100) surface. The number density of these pyramidal facets decreased to zero as the substrate misorientation angle increased to 4°. At higher misorientation angles, low angle protrusions, resembling fish scales, appeared on the surface. When the temperature was increased, facet size decreased but facet density increased. The film morphology at the high misorientations, however, improved remarkably with increasing temperature. Cross-sectional transmission electron microscopy provided evidence that both the faceted CdTe films and films with a mirror-like finish were epitaxial single crystals with no planar defects. Schwoebel barriers are suggested as the reason for the faceting of the surface grown on CdTe{100}.     

GaInAs/InP quantum wires grown by metalorganic vapor phase epitaxy on V-grooved InP substrates

A single nominally lattice matched GaInAs quantum well (QW)/quantum wire (QWR) structure was grown by metalorganic vapor phase epitaxy (MOVPE) in V-grooved InP substrates. Different Si0₂ etch masks with opening widths from 2 μm down to 200 nm (for application as second order DFB grating) were defined by optical and electron beam lithography. A damage-reduced wet chemical etching process enables the growth of the GaInAs QWs/QWRs without any InP buffer layer. In low temperature photoluminescence we found improved intensity for all wire structures prepared by this etching technique. A reduction of the period and opening width of the V-groove etch mask resulted in a optimized luminescence intensity ratio between QW and QWR. Decay times from time resolved luminescence measurements were compared to the decay times of wet or dry etched mesa wires before and after regrowth. The good optical properties of the GaInAs QWRs are encouraging for future application as a QWR-laser device.     

Pyrolysis of diisopropylantimony hydride: A new precursor for organometallic vapor phase epitaxy

The pyrolysis of diisopropylantimony hydride (DIPSbH), (C₃H₇)₂SbH, has been studied in an isothermal flow-tube reactor. The reaction products in H₂, D₂, and He carrier gases were studied using a time-of-flight mass spectrometer. T₅₀ for this compound (200‡C) is significantly lower than that of other antimony sources, such as trimethylantimony (450‡C). In addition to the hydride, the decomposition of diisopropylantimony deuteride (DIPSbD), (C₃H₇)₂SbD, was studied to provide insight into the pyrolysis mechanism. The rate limiting step was found to be first-order and is believed to be a reductive elimination reaction which produces C₃H₈ in the case of DIPSbH and C₃H₇D in the case of DIPSbD. An increase in the ratio of [C₃H₆] to [C₃H₈] was observed as the temperature was increased from 200 to 275‡C, indicating that other reactions, possibly Β-hydrogen elimination, are important as well. The reaction rate and the products produced were not affected by changing the carrier gas. The temperature dependence of the vapor pressure was determined and is described by the equation log (P)(Torr) = 7.948-2100/T(l/K).     

Optimization of selective area growth of GaAs by low pressure organometallic vapor phase epitaxy for monolithic integrated circuits

GaAs MESFET device structures have been grown on silicon nitride or silicon dioxide masked 50 and 76 mm GaAs substrates by low pressure organometallic vapor phase epitaxy. Very smooth, featureless morphology and 100 percent selectivity of GaAs islands have been achieved over a range of growth conditions. Optimization of the GaAs p-buffer of the field effect transistor structure has led to improved device performance, including increased breakdown voltage. Device characteristics of the 0.5 μm gate low noise metal semiconductor field-effect transistors fabricated on these islands show good performance and wafer to wafer reproducibility on the second device lot.     

Low oxygen and carbon incorporation in AIGaAs using tritertiarybutylaluminum in organometallic vapor phase epitaxy

High-quality AIGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al_0.25Ga_0.75As is as low as ∼2−3 × 10¹⁷ cm⁻³. Nominally undoped AIGaAs layers exhibit n-type conductiv-ity with electron concentrations at ∼ 1−1.5 × 10¹⁶ cm⁻³. A high degree of compo-sitional uniformity over 5 cm diam substrates (0.268 ±0.001) was obtained. These results indicate the potential for TTBA1 as an aluminum precursor for low temperature growth of Al-containing III-V alloys.