ZnMgSSe/ZnSSe/ZnSe-heterostructures grown by metalorganic vapor phase epitaxy

ZnMgSSe heterostructures have been grown in a low-pressure metalorganic vapor phase epitaxy system with the precursors dimethylzinc triethylamine, ditertiarybutylselenide, tertiarybutylthiol, and biscyclopentadienylmagnesium at 330°C and a total pressure of 400 hPa. The optimization of the single layers was carried out by means of low temperature photoluminescence. Only the near band edge emission was observable with negligible deep levels. The heterostructures consisting of a triple ZnSe quantum well showed intense luminescence which hints at an effective carrier confinement. Scanning transmission electron microscopy investigations of the heterostructures still showed structural detects since the layers were not lattice matched to the GaAs substrate yet.     

Optical properties and recombination mechanisms in GaN and GaN:Mg grown by metalorganic vapor phase epitaxy

Photoluminescence (PL) and reflection spectra of undoped and Mg-doped GaN single layers grown on sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) were investigated in a wide range of temperatures, excitation intensities, and doping levels. The undoped layers show n-type conductivity (μ=400 cm²/Vs, n=3×10¹⁷ cm⁻³). After annealing at T=600–700°C, the Mg-doped layers showed p-type conductivity determined by the potential-profiling technique. A small value of the full width at half maximum (FWHM=2.8 meV) of the excitonic emission and a high ratio between excitonic and deep level emission (≈5300) are evidences of the high layer quality. Two donor centers with activation energies of 35 and 22 meV were observed in undoped layers. A fine structure of the PL band with two narrow lines in the spectral range of the donor-acceptor pair (DAP) recombination was found in undoped layers. An anomaly was established in the temperature behavior of two groups of PL lines in the acceptor-bound exciton and in donor-acceptor pair regions in Mg doped layers. The lower energy line quenched with increasing temperature appreciably faster than the high energy ones. Our data does not agree with the DAP recombination model. It suggests that new approaches are required to explain the recombination mechanisms in undoped and Mg-doped GaN epitaxial layers.     

Interfaces of InAsP/InP multiple quantum wells grown by metalorganic vapor phase epitaxy

We present results of the growth of InAs_xP_1−x/InP strained heterostructures by low pressure metalorganic vapor phase epitaxy. A large incorporation of arsenic into the InAsP ternary was observed using tertiarylbutylarsine as precursor. High resolution x-ray diffraction, photoluminescence, and optical absorption measurements for InAsP/InP strained multiple quantum wells reveal that the InAsP/InP interface is very sensitive to growth interruption. A systematic study of a growth in terruption sequence designed to improve the InAs/InP interface was carried out. For nonoptimal growth interruption procedures a large density of interface states is created, probably as a consequence of compositional modifications within the interface region. We find that the absorption spectrum may reveal a significant density of interface states. Thus, photoluminescence on its own is insufficient to characterize the interface roughness even for structures showing narrow low-temperature photoluminescence peaks. We also observe an enhancement of the As content for structures grown on InP (001) relative to those simultaneously grown on InP(001) two degrees off toward [100], which suggests that the composition of As in the ternary is limited by its surface diffusion.     

Growth of high-quality GaSb by metalorganic vapor phase epitaxy

The growth of nominally undoped GaSb layers by atmospheric pressure metalorganic vapor phase epitaxy on GaSb and GaAs substrates is studied. Trimethylgallium and trimethylantimony are used as precursors for the growth at 600°C in a horizontal reactor. The effect of carrier gas flow, V/III-ratio, and trimethylgallium partial pressure on surface morphology, electrical properties and photoluminescence is investigated. The optimum values for the growth parameters are established. The carrier gas flow is shown to have a significant effect on the surface morphology. The optimum growth rate is found to be 3–8 μm/ h, which is higher than previously reported. The 2.5 μm thick GaSb layers on GaAs are p-type, having at optimized growth conditions room-temperature hole mobility and hole concentration of 800 cm² V⁻¹ s⁻¹ and 3·10¹⁶ cm^-3, respectively. The homoepitaxial GaSb layer grown with the same parameters has mirror-like surface and the photoluminescence spectrum is dominated by strong excitonic lines.     

Growth kinetics of GaSb by metalorganic vapor phase epitaxy

The growth rates of GaSb by metalorganic vapor phase epitaxy were studied as functions of growth temperatures and partial pressures of precursors. A Langmuir-Hinshelwood model was used to explain the GaSb growth rate in the chemical reaction controlled regime. The relationship between growth kinetics and epilayer qualities was discussed and properties of GaSb were obtained.     

Residual impurities in GaN/Al2O3 grown by metalorganic vapor phase epitaxy

Residual impurities in GaN films on sapphire (A1₂O₃) substrates grown by two-step metalorganic vapor phase epitaxy (MOVPE) have been investigated. We have mainly investigated the incorporation of carbon into the GaN films with GaN buffer layers on A1₂O₃ during MOVPE growth, comparing trimethygallium (TMGa) and triethygallium (TEGa) as the typical gallium precursors. The films were characterized by secondary ion mass spectroscopy analysis, photolu-minescence, and Hall measurements. The carbon, hydrogen, and oxygen concentrations increase with decreasing growth temperature in using TMGa. Especially the carbon concentration increases with decreasing a V/III ratio, for both TMGa and TEGa. There is about two times more carbon in the GaN films grown using TEGa than those using TMGa. The carbon from TMGa mainly enhances the D-A pair emission (∼378 nm), which shows the carbon makes an acceptor level at nitrogen sites in GaN. On the other hand, the carbon from TEGa enhances a deep emission (∼550 nm), which shows the carbon makes not only an acceptor level but deep levels at interstitial sites in GaN. The carbon impurities originate from methyl radicals for TMGa, or ethyl radicals for TEGa. It is supposed that, in the case of TEGa, the carbon impurities are not always located at nitrogen sites, but are also located at interstitial sites because of the C-C bonding in ethyl radicals.     

Morphology and defect structures of GaSb islands on GaAs grown by metalorganic vapor phase epitaxy

The initial nucleation of GaSb on (001) GaAs substrates by metalorganic vapor phase epitaxy has been investigated using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). TEM results showed that the GaSb islands experience a morphological transition as the growth temperature increases. For growth at 520°C, the islands are longer along the [110] direction; at 540°C, they are nearly square, and at 560°C, they are longer along the direction. Possible mechanisms are proposed to describe such a transition. TEM and HREM examination showed that lattice misfit relaxation mechanisms depend on the growth temperature. For the sample grown at 520°C, the lattice mismatch strain was accommodated mainly by 90° dislocations; for the sample grown at 540°C, the misfit strain was relieved mostly by 90° dislocations with some of 60° dislocations, and for the sample grown at 560°C, the strain was accommodated mainly by 60° dislocations which caused a local tilt of the GaSb islands with respect to the GaAs substrate. The density of threading dislocations was also found to be dependent on the growth temperature. Mechanisms are proposed to explain these phenomena.     

Electrical and optical properties of lodine doped CdZnTe layers grown by metalorganic vapor phase epitaxy

Electrical and photoluminescence properties of iodine doped CdZnTe (CZT) layers grown by metalorganic vapor phase epitaxy have been studied. Doped layers showed an n-type conductivity from the Zn composition x=0 (CdTe) to 0.07. Above x=0.07, resistivities of doped layers increased steeply up to 10⁶ Ω-cm. Resistivities of doped CZT layers were higher than those of undoped layers above x=0.6. Photoluminescence intensity of doped layers increased compared to undoped layers. Doped CdTe and ZnTe layers showed neutral donor bound exciton emission lines at the exciton related region. Also, these layers showed an increase in emission intensity at the donor acceptor pair recombination bands. Sharp emission lines were observed in doped CZT layers at around 1.49 eV. These emission lines were considered to be originated from GaAs substrates which were optically excited by the intense emission from doped CZT layers.     

Thermal annealing effects on p-type conductivity of nitrogendoped ZnSe grown by metalorganic vapor phase epitaxy

Post-growth thermal annealing (e.g., 500°C, 30 min), is proposed as one of the promising techniques to realize and to improve the quality of p-type ZnSe layers grown by metalorganic vapor phase epitaxy (MOVPE). The layers were grown at low temperature (350°C) by photo-assisted MOVPE with doping nitrogen from tertiarybutylamine (t-BuNH₂). The flow rate of t-BuNH₂ was limited to be relatively low, in order to avoid heavy doping, with which as-grown layers exhibited electrically high-resistivity; but the thermal annealing converted the layers to p-type. As the as-grown layers exhibited the stronger donor-to-acceptor pair recombination lines or the weaker donor-bound excitonic emission (I_x) lines in photoluminescence, the annealed layers resulted in higher net acceptor concentration, which was 1 x 10¹⁷ cm⁻⁴ at the optimum conditions at present.     

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.     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.     

Reconstruction of excitonic spectrum during annealing of ZnSe:N grown by metalorganic vapor phase epitaxy

The reconstruction of the bound excitonic spectra of MOVPE-grown ZnSe:N samples caused by thermal annealing was observed. The results of the low temperature photoluminescence, reflection and SIMS measurements show that this reconstruction is caused neither by the strain effect nor by the removal of hydrogen from the samples. The calculation of the defect structure and energy by the SCF MO LCAO method was carried out, and a new stable configuration of the N_se center has been found. A model of reconstruction of the nitrogen centers is proposed, assuming that the transition of N_Se centers from a less stable state with distorted T_d configuration into the energetically more favorable distorted C_3v configuration occurs due to thermal annealing, resulting in the corresponding changes in the luminescence spectra.     

Deep level transient spectroscopy assessment of silicon contamination in AlGaAs layers grown by metalorganic vapor phase epitaxy

A systematic silicon contamination has been detected by deep level transient spectroscopy in undoped and n-type doped (Te, Se, Sn) AlGaAs layers, grown in two different metalorganic vapor phase epitaxy reactors. DX center generation by substitutional donors, with very specific capture and emission thermal barriers (fingerprints), is the key to unambiguously identifying their presence, with detection limits well below the standard secondary ion mass spectroscopy capability. We comment on the potential sources of Si contamination (most common in this epitaxial technique), and on the relevance of such contamination to interpreting correctly experimental data related to the microscopic structure of DX centers.     

Highly uniform and reproducible vertical-cavity surface-emitting lasers grown by metalorganic vapor phase epitaxy with in situ reflectometry

Vertical-cavity surface-emitting lasers (VCSELs) were grown by metalorganic vapor phase epitaxy. Excellent uniformity of Fabry-Perot cavity wavelength for VCSEL materials of /spl plusmn/0.2% across a 3-in diameter wafer was achieved. This results in excellent uniformity of the lasing wavelength and threshold current of VCSEL devices. Employing pregrowth calibrations on growth rates periodically with an in situ reflectometer, we obtained a run-to-run wavelength reproducibility for 770- and 850-nm VCSELs of /spl plusmn/0.3% over the course of more than a hundred runs.     

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.     

(AlGa)As grown by low pressure metalorganic vapor phase epitaxy using a N2 carrier

We have studied the growth of Al_xGa_1−xAs (0.24<x<0.34) using a N₂ carrier in low pressure metalorganic vapor phase epitaxy. Growth temperature, gas velocity, and V/III ratio were varied to achieve optimum growth conditions. Layers with excellent morphology and electrical and optical properties comparable to samples grown using standard conditions (with a H₂ carrier) can be deposited in a nitrogen ambient. Al_0.24Ga_0.76As bulk material grown on an AlAs buffer layer with a background doping of 1.3×10¹⁶ cm⁻³ showed Hall mobilities of 4500 and 2300 cm²/Vs at 77 and 300K. Photoluminescence studies at 2K revealed strong bound exciton transitions with a full width at half maximum of 5.2 meV for Al_0.29Ga_0.71AS.     

Interdiffusion and relaxation in metalorganic vapor phase epitaxy grown InGaAs/GaAs strained layer quantum wells

Low pressure metalorganic vapor phase epitaxy grown strained InGaAs/GaAs quantum well structures have been characterized by photoluminescence and x-ray diffraction. It is shown that beyond the pseudomorphic limit, these structures show considerable gallium/indium interdiffusion at the interfaces and partial strain relaxation in the quantum well layers.     

Excitonic properties of Zn1−xCdxSe/ZnSe quantum well structures grown by metalorganic vapor phase epitaxy

This paper presents optical characteristics of Zn_0.82Cd_0.18Se/ZnSe single quantum well (SQW) structures grown by a low-pressure metalorganic vapor-phase epitaxy. The excitonic optical absorption and emission properties are studied by electroreflectance, photocurrent, and photoluminescence (PL) spectrum measurements under controlled high electric fields. The PL spectrum shows a considerable red shift (up to 20 meV) against the ground state of the heavy-hole exciton in the SQW, and is quite iN_Sensitive to the applied high electric field (>10⁴V/cm). The results have indicated that the exciton responsible for the photon emission process (spontaneous/stimulated) is different from the ground state of the heavy-hole exciton, which is responsible for the photon absorption process.     

Characterization of InGaAs/GaAs(001) films grown by metalorganic vapor phase epitaxy using alternative sources

Thin films of In_xGa_1−xAs (0<x<0.012) on GaAs (001) were grown by metalorganic vapor phase epitaxy using triisopropylindium, triisobutylgallium, and tertiarybutylarsine. The effect of the process conditions, temperature, and V/III ratio on the film quality was studied using high resolution x-ray diffraction, scanning tunneling microscopy, and Hall measurements. High quality films were grown at temperatures as low as 475 °C and at a V/III ratio of 100. However, under these conditions, a change in growth mode from step flow to two-dimensional nucleation was observed.