Pressure Organometallic Vapor Phase Research Articles

Organometallic vapor phase epitaxy of GaN on Si(1 1 1) with a γ-Al 2O 3(1 1 1) epitaxial intermediate layer

Heteroepitaxial growth of GaN on Si(1 1 1) substrate was investigated by atmospheric pressure organometallic vapor-phase epitaxy. High-quality GaN layers on Si were deposited using an epitaxially grown intermediate layer of γ-Al 2O 3. The orientation relationship was found to be GaN(0 0 0 1)/γ-Al 2O 3(1 1 1)/Si(1 1 1) and GaN[1 1 2 ̄ 0]∥ γ-Al 2 O 3[ 1 ̄ 1 0]∥ Si[ 1 ̄ 1 0] . GaN layers with (0 0 0 2) rocking curve line width of 1000 arcsec have been obtained.

Effects of multiple buffer layers on structural electronic properties of GaN growth by atmospheric pressure Organometallic Vapor Phase Epitaxy

High-quality GaN epitaxial films have been grown on sapphire by organometallic vapor phase epitaxy using multiple-pair buffer layers. Each pair of buffer layers consists of a thin GaN nucleation layer grown at a low temperature around 500°C and a thick GaN epitaxial layer around 4 μm thick grown at a high temperature around 1000°C. The sample with four-pair buffer layers showed much improved GaN epitaxial films, as compared to the sample with only one-pair of buffer layers. The better qualities include narrower full width at half maximum of 150 arc-s and stronger intensity in double-crystal X-ray diffraction, higher electron mobility of 420 cm 2 V-s −1, lower background concentration of 3×10 17 cm −3, and lower etch-pit density of mid-10 5 cm −2.

Highly p-type carbon-doped InGaAs grown by atmospheric pressure organometallic vapor-phase epitaxy

Carbon doped, p-type, In x Ga 1− x As (0.2< x<0.65) epilayers have been grown on InP substrates at relatively low temperature (450°C) using atmospheric pressure organometallic vapor-phase epitaxy (APOMVPE). Excellent morphology was obtained in all cases. After growth van der Pauw–Hall measurements revealed high hole concentrations in the range 8.5×10 18–8.7×10 19 cm −3 (highest reported to date for APOMVPE). The effects of growth temperature, V/III ratio and CCl 4 partial pressure on the carrier concentration and mobility are reported. X-ray diffraction reveals excellent crystal quality. Annealing the samples in different ambients at 400–500°C caused no significant variation in the carrier concentration or mobility, i.e. minimal dopant ion passivation was measured. However, reversible hole compensation was measured after annealing at 650°C. This suggests that macroscopic defects probably are associated with carrier compensation.

Influences of initial nitridation and buffer layer deposition on the morphology of a (0001) GaN layer grown on sapphire substrates

Hexagonal GaN is grown on (0001) sapphire substrates using an atmospheric pressure organometallic vapor phase epitaxy method. We investigate the influences of the initial treatment of sapphire substrate, such as initial nitridation and low-temperature GaN buffer layer deposition, upon the surface morphology and crystallinity. The thermal stability of grown GaN layers is also investigated using a thermal etching process in a H2 atmosphere in order to obtain the information concerning the surface polarity of GaN(0001) layers. When sapphire substrates are initially nitrided, highly crystalline GaN layers with large hexagonal facets are obtained and its surface appears to be (0001)N. On the other hand, the deposition of a thicker buffer layer on the nitrided sapphire substrates improves the surface morphology, and the surface polarity of the mirror surface appears to be (0001)Ga. The initial nitridation of sapphire substrates and the GaN buffer layer deposition are considered to be important processes from viewpoints of the (0001) surface polarity.

Photoluminescence characterization of GaN thin film grown by atmospheric pressure organometallic vapor phase epitaxy

Thin films of gallium nitride (GaN) were successfully prepared by our atmospheric pressure (AP) organometallic vapor phase epitaxy (OMVPE) system using GaN buffer layer over basal plane (0001) sapphire substrates. In the present study, strong band-edge photoluminescence (PL) in GaN films is observed. The variations of the growth temperature and ammonia/trimethylgallium (NH 3/TMG) mass flow ratio with the full width at half maximum (FWHM) of band-edge luminescence ( I BE, respectively, indicate that we could obtain ranges of the growth temperature and the NH 3/TMG ratio to have high quality GaN single crystal. The band-edge to deep-level luminescence ( I DL) ratio ( I BE/ I DL) also reveals that we could obtain optimized appropriate growth temperature and the supply of active nitrogen of excellent optical properties.

Very high hole concentrations in C-doped InGaAs using new sources with APOMVPE

AbstractNew sources have been used to grow the first carbon doped, highly p-type InxGa1-xAs (0.2&gt;x&gt;0.7) epilayers on InP substrates by atmospheric pressure organometallic vapor phase epitaxy (APOMVPE). Excellent morphology was obtained simultaneously with high hole concentrations at growth temperatures near 450 °C. High hole concentrations of 1.6×1019 – 8.7×1019 cm−3 (the highest reported to date for APOMVPE), and the corresponding room temperature hole mobilities of 65 – 25 cm2/s, respectively, have been obtained from Hall measurements. X-ray diffraction is consistent with excellent crystal quality. Annealing at temperatures of T=400–500 °C in the presence of either nitrogen or hydrogen was found to change the carrier concentration by only 0–15%. However, after annealing at T=650 °C, irreversible changes occurred in the InGaAs. After a high temperature anneal, reversible order of magnitude changes in the hole concentration was obtained upon further annealing at low temperatures, depending upon the ambient. These results conclusively show that hydrogen does not passivate C acceptor ions in InGaAs. Since changes in the carrier concentration become substantial and reversible only after high temperature annealing, the results strongly suggest that a structural change occurred in the crystal at high temperatures. We consider it likely that this structural change is the precipitation of carbon out of a supersaturated solid solution, and that hydrogen atoms associated with these precipitates act as donors which compensate the hole concentration.

Diffraction-limited 1.3-μm-wavelength tapered-gain-region lasers with &gt;1-W CW output power

Diode lasers have been fabricated in InGaAsP-InP multiple-quantum-well material grown by atmospheric-pressure organometallic vapor-phase epitaxy with an active optical cavity consisting of a ridge-waveguide region coupled to a tapered gain region. Over 1 W of CW output power was obtained with 85% of the power in the central lobe of a diffraction-limited far-field radiation pattern.

Growth by OMVPE and X-ray analysis of ZnTe and [formula omitted] epilayers on III–V substrates

II–VI compounds are promising materials for optoelectronic applications. They are characterized by a large bandgap in the visible region, which allows the production of lasers and light emitting diodes in the blue region as the zinc telluride gap at room temperature is 2.26 eV. We studied the epitaxial growth of zinc telluride and zinc selenide epilayers on gallium arsenide, indium phosphide and gallium arsenide substrates by atmospheric pressure organo-metallic vapor phase epitaxy. We focused especially on the X-ray analysis of thin layer deformations. The relaxation of the deformation in ZnTe epilayers on InP substrates and ZnSe buffer is abrupt. We observed serious deformation of the thin layers on a GaSb substrate.

InTlSb growth by OMVPE

We report on the growth of InTlSb at various temperatures by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Electron microprobe analysis indicates that the Tl solubility is < 1 at% in InSb at growth temperatures of 400–475°C. This is in gross disagreement with a recently calculated pseudobinary phase diagram which predicts a solubility limit of ∼ 15%. Although the epilayers grown were shiny to the naked eye, a microscopic quantity of a second condensed phase was observed. A series of simple experiments was designed and performed to experimentally construct portions of the InTlSb isothermal ternary phase diagram. We demonstrate that typical OMVPE growth conditions lie in a three-phase region bounded by InSb, metallic Sb, and liquid In + Tl + Sb. The limited Tl solubility in InSb is due to the very low stability of TlSb relative to the liquid phase.

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.

Investigation of chemical wet-etch surface modification of Ga0.5In0.5P using photoluminescence , x-ray photoelectron spectroscopy, capacitance measurements, and photocurrent-voltage curves

Epitaxial Ga[sub 0.5]In[sub 0.5]P films, deposited lattice-matched to GaAs by atmospheric pressure organometallic vapor phase epitaxy, were subjected to various wet-etching processes and the resulting surface was characterized. The steady-state photoluminescence (PL) peak intensity was found to increase 5-fold with some etches, indicating lowered surface recombination rates as a result of etching. Average PL decay times estimated from time-resolved photoluminescence studies also exhibited a correspondingly significant enhancement. Capacitance-voltage and photocurrent-voltage measurements were carried out to investigate changes in energetics of the band edges or alteration in kinetics as a result of the treatments. High resolution X-ray photoelectron spectroscopy revealed a variation of the oxidized species of P, Ga, and In on the surface with etching and were correlated to the PL results. The amount of oxidized material on the surface was lowered after etching in concentrated H[sub 2]SO[sub 4], 1:20:1 HCl:CH[sub 3]COOH:H[sub 2]O[sub 2], and 1:20:1 HCl:H[sub 3]PO[sub 4]:H[sub 2]O[sub 2] and concurred with observations of a higher steady-state PL intensity and longer carrier lifetimes. A nitric acid or aqua regia etch on the other hand yielded an oxide-rich surface with diminished PL. 30 refs., 10 figs., 2 tabs.

Photoluminescence process in AlP/GaP short period superlattices grown by organometallic vapor phase epitaxy using tertiarybutylphosphine

Photoluminescence (PL) processes in (AlP) m /(GaP) m ( m=1–8 monolayers (ML)) short period superlattices grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) using tertiarybutylphosphine (TBP) are investigated. Strong emission of bound excitons without phonon replicas is observed at low temperature. This suggests that the luminescence processes are of a direct transition. The transition probability is found to be very small since there is no band edge emission at high temperature. For the AlP/GaP superlattices with monolayer numbers greater than 4, the structural dependence of PL properties such as peak position and intensity qualitatively agree with the theoretically predicted results. However, direct to indirect transitions which are theoretically predicted for smaller monolayer numbers are not observed.

Structure and photoluminescence of AlP/GaP short-period superlattices grown by organometallic vapor phase epitaxy

Short-period superlattices of (AlP)m/(GaP)n (m, n=4–11.5) are grown by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine as a phosphorus source. Structural and optical properties of the grown superlattices are characterized by double-crystal x-ray diffraction and photoluminescence (PL) measurements, respectively. By comparing the measured and the calculated full width at half-maximum of satellite peaks, we find that very high quality superlattices with atomically abrupt heterointerfaces are achieved. Strong emission of bound exciton is observed at low temperature. The exciton emission, however, disappears quickly as the temperature is increased, and only PL lines due to impurity recombination remain at high temperature (≳30 K). No evident phonon replica is observed in the PL spectra. From these results, a direct band-gap structure seems to be realized as expected from the zone-folding effect. However, the absence of band-to-band direct transition at high temperature suggests that the direct transition probability between the zone-folded conduction band and the valence band is not so large.

Use of germanium interfacial layer for the hetero-epitaxial growth of CdTe on Si substrates

Epitaxial (100) CdTe layers have been grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) on Si(100) substrates misoriented 9° towards the (110) direction. A thin Ge buffer layer grown at low temperature followed by an interfacial layer of ZnTe was used to get high quality (100) CdTe. The layers were characterized by X-ray diffraction and optical microscopy. X-ray rocking curve with FWHM of about 260 arc sec has been obtained for a 4 μm thick CdTe layer. The results presented demonstrate a novel technique to grow high quality CdTe on Si in a single OMVPE reactor.

Control of ordering in GaInP and effect on bandgap energy

GaxIn1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with 10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure (ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm deep) grooves, with maximum angles of 1 μm2 cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence (CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition demonstrate that the shift in emission energy is not due to changes in solid composition. This is the firstdirect verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga0.5In0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several orders of magnitude.

Growth of (100) oriented CdTe on Si using Ge as a buffer layer

Epitaxial (100) CdTe layers have been grown on (100) oriented Si substrates by atmospheric pressure organometallic vapor phase epitaxy using thin Ge as a buffer layer. A very thin native oxide layer may be present on Si substrates after etching in a HF solution and this can be removed by passing GeH4 gas over Si at 450 °C. The removal of this oxide takes several minutes depending on the oxide layer thickness and reactor conditions. For the CdTe layers grown on Ge/Si substrates, single-crystal (100) CdTe can be obtained at growth temperatures higher than 420 °C. For growth temperatures below 420 °C, a mixture of both (100) and (111) oriented CdTe was present. The x-ray full width at half-maximum of the (400) peak was 780 arcsec for a 3.1-μm-thick CdTe layer grown at 450 °C with a Ge buffer. Although all the layers had antiphase domains, single-domain CdTe can be grown on (100)Si misoriented towards [110]. This result presents an alternative for nucleating CdTe on Si without a GaAs buffer layer.

InAsBi alloys grown by organometallic vapor phase epitaxy

InAsBi is a III/V alloy with potential application for detectors in the 8–12 μm region of the spectrum. Growth of InAs 1- x Bi x , with x ≤ 0.054, at 350°C by atmospheric pressure organometallic vapor phase epitaxy has been made possible by using a new combination of precursors, ethyldimethylindium (EDMIn), tertiarybutylarsine (TBAs) and trimethylbismuth (TMBi). Results were obtained using a V/III ratio between 21 and 22. With these conditions, a Bi distribution coefficient of 1.746 was measured. X-ray diffraction verifies that Bi incorporates substitutionally into the zincblende structure. For x < 0.045, it was possible to suppress whisker formation and obtain excellent surface morphology. Measurement of photoluminescence for x ≤ 0.037 indicates good crystal quality. The measured rate of change of bandgap with Bi concentration, d E g/d x = -55 meV/%Bi, indicates that a 77 K bandgap energy of E = 0.10 eV should be reached with an alloy composition of InAs 0.94Bi 0.06.

Band-gap narrowing in ordered Ga0.47In0.53As

We report the first observation of band-gap energy reduction in Ga0.47In0.53As deposited on (100) InP by atmospheric pressure organometallic vapor phase epitaxy due to CuPt-type ordering. A reduction of more than 65 meV in the band-gap energy is observed for lattice-matched samples that show strong CuPt-like ordering by transmission electron microscopy. By comparison samples that show no CuPt-like ordering diffraction signatures, do not have reduced band-gap energies. Studies of the influence of growth parameters on the band-gap energy indicate a U-shaped dependence on the growth temperature with a minimum around 550 °C and decreasing band-gap energies with increasing growth rate (at a constant V/III ratio) over the range 0.5–4 μm/h.

Strong photoluminescence from AlP/GaP disordered superlattice grown by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine

AlP/GaP disordered superlattices (d-SLs) are grown for the first time by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine as the phosphorous source. Strong photoluminescence (PL) is observed from the d-SL, comparing with the ordered superlattice (o-SL) and the bulk alloy (b-AL). The PL intensity of the d-SL is 158 times stronger than that of the o-SL and 114 times than that of the b-AL. The strong PL from the d-SL is attributed to the localized states created by the artificial disordering.

Epitaxial growth of AlGaInP lattice-matched to GaAsP substrates by organometallic vapor phase epitaxy

Ga 0.7In 0.3P is grown on GaAs 0.62P 0.38 substrates by atmospheric pressure organometallic vapor phase epitaxy and characterized with photoluminescence spectroscopy, double-crystal X-ray diffraction and transmission electron microscopy. The layers are free form defects when examined by transmission electron microscopy. They show bright orange, yellow and yellow green photoluminescence depending on composition. High quality (Al 0.7Ga 0.3) 0.7In 0.3P closely lattice-matched to the GaAsP substrate is also grown and doped with Si and Zn.