Pressure Organometallic Vapor Phase Epitaxy Research Articles

Quantum size microcrystals grown using organometallic vapor phase epitaxy

Needle-shaped quantum size microcrystals as thin as 10 nm have been selectively grown by employing reduced pressure organometallic vapor phase epitaxy using trimethylgallium and arsine as source materials. The microcrystals grown within a SiO2 window area have their growth axes along the [111] direction. Transmission electron diffraction analysis shows that the crystal structure of microcrystals is consistent with the zinc-blende structure of GaAs. The mechanism for growing the needle-shaped crystals is similar to a vapor-liquid-solid (VLS) equilibrium phase growth model. From photoluminescence measurements at 4.2 K, it is found that the microcrystals show a very distinct spectra for free exciton and neutral acceptor-bound exciton recombinations, meaning good crystal quality.

Optical properties of InAs/InP strained single quantum wells grown by organometallic vapor-phase epitaxy

The optical emission characteristics of highly strained InAs/InP single quantum wells prepared using atmospheric-pressure organometallic vapor-phase epitaxy have been studied. For well thicknesses of one to three monolayers (ML), the photoluminescence (PL) spectra exhibited intense emission in the energy range 1.15–1.3 eV, with typical full width at half maximum of 8–14 meV. The dependence of PL emission energy on well thickness for 1–5-ML-thick wells was compared with the results of a finite-well calculation, taking into account the effects of strain on the band structure. Good agreement between experiment and theory was obtained for a valence-band offset of 270 meV, consistent with recent reports for the InAs/InP system.

The use of triisopropylantimony for the growth of InSb and GaSb

A newly developed Sb source, triisopropylantimony (TIPSb), has been successfully used to grow InSb and GaSb epilayers by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Both GaSb and InSb have been grown with excellent morphologies. Growth efficiencies indicate that there are no parasitic reactions between TIPSb and trimethylgallium (TMGa) or trimethylindium. For GaSb growth, the temperatures have been varied between 500 and 600 °C. V/III ratios close to unity are necessary to obtain the best morphologies at 600 °C. As the growth temperature is decreased, lower V/III ratios are required. This is because TMGa decomposition is incomplete and TIPSb decomposes completely at these temperatures. The GaSb layers grown at 500 °C have background hole concentrations of 2×1016 cm−3. Low-temperature photoluminescence (PL) measurements indicate that the acceptor is due to Sb vacancies rather than carbon acceptors. A major advantage of TIPSb is that it decomposes at temperatures much lower than that for trimethylantimony (TMSb). InSb with good morphologies can be grown using V/III ratios close to unity at temperatures as low as 430 °C. On the other hand, growth temperatures higher than 500 °C are necessary for the growth of InSb using TMSb with V/III ratios of close to 1. For temperatures lower than 430 °C, InSb can be grown using TIPSb, but higher V/III ratios are required due to incomplete TIPSb pyrolysis. The InSb epilayers have electron concentrations of about 5×1016 cm−3 at 77 K and low-temperature PL shows well-resolved exciton and acceptor-related peaks. These results indicate that TIPSb is a viable source for the OMVPE growth of Sb-containing III-V semiconductors.

GaInP/AlGaInP strained quantum wells grown using atmospheric pressure organometallic vapor phase epitaxy

Single and multiple Ga0.4In0.6P/(Al0.4Ga0.6)0.5In0.5P quantum wells (QWs) have been grown using atmospheric pressure organometallic vapor phase epitaxy. The Ga0.4In0.6P well layers are coherently strained to match the lattice parameter of the GaAs substrate. Transmission electron microscopy measurements indicate that the QW layers are uniform in thickness and the interface is abrupt and free of misfit dislocations and defects. An upshift in photoluminescence (PL) peak energy is observed as the thickness of the well layer decreases, due to carrier confinement in the QW. Higher order X-ray diffraction satellite peaks and a narrow PL halfwidth are observed in a 20 layer multiple quantum well sample, indicating that the strained QWs are of high quality and the composition and thickness are under precise control during the growth process. Considering the effect of strain on the heterojunction band offsets, the PL peak energy of the strained QW can be described by a simple theory as a function of the well width.

High-Conductance GaAs Tunnel Diodes by OMVPE

ABSTRACTGaAs p+-n+ tunnel diodes have been grown by atmospheric-pressure organometallic vapor phase epitaxy (OMVPE) using zinc as the dopant for the p+ regions and either Se or Si as the dopant for the n+ regions. At a growth temperature of 700° C, using a “cycled” growth for just the Zn-doped p++-GaAs layer both the conductance and the peak current of the tunnel diode has been increased by a factor of ˜65. The conductance of the tunnel diode, maximized at a growth temperature of 650 °C with the cycled growth, is comparable to the best reported values by MBE. Cycled growths for n+ Se-doped regions reduce the tunnel-diode conductance by more than two orders of magnitude. However, the cycled growth for n+-GaAs regions formed with Si doping shows no conductance degradation. A model for these observations is presented.

InAs/InP strained single quantum wells grown by atmospheric pressure organometallic vapor phase epitaxy

Strained InAs/InP single quantum wells of nominal thickness 1–11 monolayers have been prepared using organometallic vapor phase epitaxy in an atmospheric pressure reactor. For wells of thickness 1–3 ML grown using optimal flow modulation parameters, the surface morphology was specular and narrow single-line photoluminescent emission was observed. For thicker wells, the evolution of additional PL features and the appearance of island-like features on the sample surface was attributed to the onset of three-dimensional (island) growth.

Organometallic vapor-phase epitaxy growth and characterization of Bi-containing III/V alloys

For potential infrared detector applications, single-crystalline InAsBi and InAsSbBi have been grown by atmospheric pressure organometallic vapor-phase epitaxy. The precursors used were trimethylindium, trimethylantimony, trimethylbismuth, and arsine at growth temperatures of 375 and 400 °C. Good quality epilayers with smooth surface morphologies were obtained by properly controlling the key growth parameter, the V/III ratio. The variation of lattice constant with solid composition for the InAs1−xBix system, a=6.058+0.966x, provides evidence that Bi atoms indeed incorporate substitutionally into the As sites of the sublattice in the InAs zinc-blende structure. An extrapolated lattice parameter for the hypothetical zinc-blende InBi is 7.024 Å. Thermodynamic calculations of the InAs-InBi and InSb-InBi pseudobinary phase diagrams were carried out using the delta-lattice-parameter model using the lattice constant for zinc-blende InBi of 7.024 Å. The results agree well with experimental data. The calculations predict that the solid solubility limit of Bi in InAs is less than 0.025 at. %. The calculated maximum solubility limit is 2.1 at. % for Bi in InSb at the eutectic temperature of 132 °C. Thus, tremendously large miscibility gaps exist in both alloy systems. The critical temperature was predicted to be 2569 °C for the InAs-InBi system and 496 °C for the InSb-InBi system. The miscibility gap is the major factor limiting Bi incorporation into the InAsSb alloys. Nevertheless, metastable InAsBi and InAsSbBi alloys were grown with concentrations far exceeding the solubility limit. For example 3.1 at. % Bi was incorporated into InAs. Infrared photoluminescence measurements show a decrease of peak energy with increasing Bi concentration in the alloys, with dEg/dx=−55 meV/at. %Bi.

Organometallic vapor phase epitaxial growth of a new quarternary semiconductor alloy Ga 1− xIn xP 1− ySb y

Quaternary Ga 1− x In x P 1− y Sb y alloys have been grown for the first time by atmospheric pressure organometallic vapor phase epitaxy (AP-OMVPE) in a horizontal, infrared-heated reactor using trimethylgallium, trimethylindium trimethylantimony, and phosphine as the source materials. In general, epilayers with good surface morphologies were obtained. Growth temperatures between 480 and 560°C were used because of the low melting temperatures of these alloys. At the lower end of this range, Ga incorporation was found to decrease with decreasing temperature. Furthermore, the presence of Sb in the growth process also caused a decrease of the Ga distribution coefficient. Optical characterization was carried out using low temperature photoluminescence, photoluminescence excitation, and transmission spectroscopies. Quaternary alloys with 10 K energy band gaps ranging from 0.21 to 1.98 eV (5.9 to 0.63 μm) were grown on GaAs, InP, GaSb, InAs, and InSb substrates. The band gap energies were found to be in good agreement with the results of earlier calculations. However, 10 K photoluminescence of Ga 1− x In x P 1− y Sb y with higher band gaps was routinely observed with peak energies about 90 to 140 meV lower than the band gap energies. This may be due to either donor-acceptor pair recombination or, perhaps, recombination involving tail states produced by compositional fluctuations in these highly metastable alloys. Smaller band gap alloys have peak energies lower than the values of band gap by about 20 to 110 meV.

Optical absorption and emission of InP1−xSbx alloys

A detailed optical study of the metastable III/V semiconductor alloy InP1−xSbx is presented. InP1−xSbx layers are grown throughout the entire compositional range by atmospheric pressure organometallic vapor phase epitaxy on InP, InAs, and InSb substrates. Composition and strain are measured by combined electron microprobe analysis and x-ray diffractometry. The dependence of band gap on composition is experimentally established for the first time from absorption spectra measured at 10 and 300 K. The resultant value of the band-gap bowing parameter is 1.52±0.08 eV, independent of temperature. The absorption spectra show the InP1−xSbx layers to have long band tails, which extend further into the gap as the Sb concentration is increased. The band tails are induced by compositional clustering. Photoluminescence (PL) spectra are measured between 10 and 300 K. The PL peaks are assigned to recombination between carriers occupying band-tail states or to recombination via deep centers in the gap.

Improved 1.5 μm wavelength lasers using high quality LP-OMVPE grown strained-layer InGaAs quantum wells

Strained-layer (SL) In x Ga 1− x As/ InP and In x Ga 1− x As/ InGaAsP QWs with 1.8% biaxial compressive strain have been grown by low pressure organometallic vapour phase epitaxy on 0.2° and 2° misoriented (001) InP substrates in the same growth run. The SL QWs grown on 2° misoriented substrates showed broad photoluminescence lines due to well width variations of about a factor of 2 resulting from 3D-like growth as revealed in TEM, whereas the corresponding SL QWs grown on 0.2° misoriented substrates showed narrow multiple line photoluminescence emissions. These multiple lines are ascribed to (half)-monolayer well width variations within one QW with atomically flat interfaces over areas larger than the excitonic diameter. SL-modulation-doped In x Ga 1− x As/ InGaAsP QWs were used to manufacture 1.5 μm wavelength DCPBH laser diodes. For the first time, significantly improved device characteristics were obtained. A differential external efficiency as high as 82%, a characteristic temperature as high as 97 K and CW output powers as high as 200 mW were measured. The improved device performances are ascribed to the strain-induced reduction of non-radiative recombination in the structures. Lifetests performed at 60°C heat-sink temperature and a CW output power of 5 mW showed almost no degradation after 4000 h.

Atomspheric pressure organometallic vapor-phase epitaxial growth and characterization of Ga0.4In0.6P/(Al0.4Ga0.6)0.5In0.5P strained quantum wells

Single and multiple Ga0.4In0.6P/(Al0.4Ga0.6)0.5In0.5P quantum wells have been grown using atmospheric pressure organometallic vapor phase epitaxy. The Ga0.4In0.6P well layers are coherently strained to match the lattice parameter of the GaAs substrate. Transmission electron microscopic results showed that the quantum-well layers are very uniform in thickness and the interface is abrupt and free of misfit dislocations. The photoluminescence peak energy increases as the well width decreases, due to carrier confinement in the quantum well. Growth interruptions do not change the photoluminescence peak energy of the quantum well. However, the photoluminescence intensity is drastically reduced for longer growth interruption times. Higher-order x-ray diffraction satellite peaks and a narrow photoluminescence halfwidth are observed in a 20-layer multiple-quantum-well sample, indicative of high structural uniformity and precise control of the composition and thickness during the growth process. Considering the effect of strain on the heterojunction band offsets, the photoluminescence peak energy of the strained quantum well can be described by a simple theory as a function of the well width.

Atmospheric pressure organometallic vapor phase epitaxy growth of high-mobility GaAs using trimethylgallium and arsine

Epitaxial layers of GaAs with peak mobilities as high as 200 000 cm2/V s at 50 K have been grown in an atmospheric pressure organometallic vapor phase epitaxy reactor using trimethylgallium (TMG) and arsine. The growth conditions which lead to high-mobility GaAs are described in this letter. Low-temperature photoluminescence and temperature-dependent Hall measurements are used to study the dependence of the incorporation of residual impurities on the growth temperature and arsine partial pressure. Carbon acceptor densities <1014 cm−3 were measured in the highest purity samples.

Photoluminescence of InAsBi and InAsSbBi grown by organometallic vapor phase epitaxy

Infrared photoluminescence (PL) from InAsBi and InAsSbBi epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been studied. The PL from ternary InAsBi was investigated for Bi concentrations of ≤2.3 at. %. The peak energy decreases at a rate of 55 meV/at. % Bi with increasing Bi concentration. A study of the transmission spectra of these Bi-containing alloys confirms the above result. The PL peak is assigned to near band edge emission for InAsBi. The value of dEg/dx=−55-meV/at. % Bi is more than double the previously reported theoretical prediction for the band gap of InAsBi. The PL for the quaternary layer of InAsSbBi is also studied for Sb concentrations of <10 at. % and Bi concentrations of ≤1.5 at. %. Bi incorporation in InAs1−xSbx(0.07<x<0.10) reduces the PL peak energy at a rate of 46-meV/at. % Bi. These results imply that incorporation of only a few percent of Bi is required in InAs0.35Sb0.65 to achieve a band gap of 0.1 eV, equivalent to a wavelength of 12 μm, desired for infrared detector applications.

Optical absorption and emission of GaP1−xSbx alloys

The first detailed optical investigation of the metastable III/V semiconductor alloy GaP1−xSbx is presented. Epilayers are grown by atmospheric pressure organometallic vapor phase epitaxy throughout the entire compositional range on GaP, GaAs, and GaSb substrates. The approximately 1-μm-thick layers are partially strained with values of lattice mismatch as large as 1.7×10−2. Values of band gap are determined for the first time from absorption spectra measured at 10 and 300 K and corrected for strain-induced energy shifts. The resultant values of bowing parameter for the direct and indirect band gaps are cΓ=3.11±0.18 eV and cx =2.06±0.18 eV, independent of temperature, yielding a value of direct/indirect crossover composition, xc, of 0.32±0.07. Single photoluminescence (PL) peaks are observed between 10 and 300 K for all samples. For samples with 0.37≤x≤0.47, they are assigned to recombination of carriers localized in bandtail states induced by compositional fluctuations. The stretch of the tails into the gap is greatly enhanced over the random alloy limit by the metastability of the Ga1−xSbx alloys. PL peaks for samples with x≤0.32 are assigned to recombination via deep centers in the gap. The PL peak of a sample with x=0.91 is assigned to recombination involving shallow acceptors.

Photoluminescence of InSb, InAs, and InAsSb grown by organometallic vapor phase epitaxy

Infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x<0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range. The values of full width at half maximum of the PL peaks show that the epitaxial layer quality is comparable to that grown by molecular-beam epitaxy. The observed small peak shift with temperature for most InAs1−xSbx epilayers may be explained by wave-vector-nonconserving transitions involved in the PL emission. For comparison, PL spectra from InSb/InSb and InAs/InAs show that the wave-vector-conserving mechanism is responsible for the PL emission. The temperature dependence of the energy band gaps, Eg, in InSb and InAs is shown to follow Varshni’s equation Eg(T)=Eg0−αT2/ (T+β). The empirical constants are calculated to be Eg0=235 meV, α=0.270 meV/K, and β=106 K for InSb and Eg0=415 meV, α=0.276 meV/K, and β=83 K for InAs.

Transmission electron microscope characterization of AlGaInP grown by organometallic vapor phase epitaxy

AlGaInP epitaxial layers grown at 690 °C by atmospheric pressure organometallic vapor phase epitaxy are investigated by transmission electron microscopy. For the first time, compositionally modulated and ordered structures are simultaneously observed in AlGaInP alloys. The ordering is of the CuPt type with ordering along the {111} directions. The ordered regions appear as plate-like microdomains, while the composition modulation takes the form of a fine columnar constrast oriented along the growth direction. In addition, from the results of (001) plan-view diffraction contrast examination, the principal strain direction associated with the modulation structures is found to be perpendicular to the growth direction and lies in the surface plane. Thus, it is concluded that the spinodal decomposition is initiated and developed on the surface during the growth of the AlGaInP epitaxial layers and, finally, forms the columnar structure.

Effect of operating conditions and precursors on optoelectronic properties of OMVPE grown ZnSe

The growth of ZnSe on (100)GaAs substrates by low pressure organometallic vapor phase epitaxy (OMVPE) has been investigated in a vertical reactor. Dimethylzinc (DMZn) was used as the Zn precursor, while three selenium sources were employed: diethylselenide (DESe), methylallylselenide (MASe) and hydrogen selenide (H 2Se). Films grown at the optimal conditions, corresponding to each source combination, contain different impurities. The optically active impurities are analyzed by comparing photoluminescence spectra of as-grown films. The source combination H 2Se/DMZn produces the best quality ZnSe epilayers. The effect of operating conditions on the electrical and photoluminescence properties of films grown from H 2Se/DMZn is examined. Chlorine is determined to be the major shallow donor impurity of these films and an increase in the growth temperature is demonstrated to be a simple way to control the residual chlorine impurities. Finally, a relationship between electrical properties and photoluminescence characteristics is proposed and examined in view of data from this study as well as from previously reported OMVPE and molecular beam epitaxy (MBE) studies.

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

Selective area epitaxial growth of Ga0.47In0.53As 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°.

Low degradation rate in strained InGaAs/AlGaAs single quantum well lasers

A 10000 h, 30 degrees C constant-current lifetest performed on five strained In/sub 0.2/Ga/sub 0.8/As/AlGaAs single-quantum-well lasers, with lambda approximately 930 nm, is discussed. The devices are 90- mu m*400- mu m oxide-stripe lasers with facet coatings, grown by atmospheric pressure organometallic vapor-phase epitaxy. For each diode, the current was maintained at a constant value of approximately 300 mA, corresponding to approximately 100 mW of output power. After 10/sup 4/ h, thresholds increased from an average of 84 mA to 108 mA, while quantum efficiencies were essentially unchanged. In relation to a typical 100-mW constant-power lifetest, this is equivalent to a degradation rate of less than 1%/kh. >

980 nm diode laser for pumping Er/sup 3+/-doped fiber amplifiers

A high-power 980-nm diode laser, whose performance satisfies the requirements for pumping Er/sup 3+/-doped optical fiber amplifiers, is described. The device is grown by atmospheric pressure organometallic vapor-phase epitaxy and contains a strained, step-graded In/sub 0.25/Ga/sub 0.75/As/AlGaAs single-quantum-well active region. The threshold current of the ridge-waveguide laser is 8 mA, and a CW power output of 125 mW with a different quantum efficiency of 59% is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>