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1.
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.  相似文献   

2.
The growth rates of CdTe and HgCdTe by hot wall metalorganic vapor phase epitaxy were studied as functions of growth temperatures and partial pressures of precursors. It is suggested that the growth of CdTe and HgCdTe was controlled by reaction kinetics. The relationship between growth processes and epilayer properties was discussed and high quality epilayers were obtained.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
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.  相似文献   

6.
The growth characteristics of thick (100) CdTe epitaxial layers of a thickness up to 200 μm on a (100) GaAs substrate in a metal-organic vapor-phase epitaxy (MOVPE) system and fabrication of CdTe/n+-GaAs heterojunction diodes for their possible applications in low-energy x-ray imaging detectors are reported. The grown epilayers were of high structural quality as revealed from the x-ray double-crystal rocking curve (DCRC) analysis, where the full-width at half-maximum (FWHM) values of the (400) diffraction peaks was between 50 arcsec and 70 arcsec. The 4.2-K photoluminescence (PL) showed high-intensity bound-excitonic emission and very small defect-related peaks. The heterojunction diode fabricated had a good rectification property with a low value of reverse-bias current. The x-ray detection capability of the diode was examined by the time-of-flight (TOF) measurement, where good bias-dependent photoresponse was observed, but no carrier transport property could be deduced. It was found that the CdTe layer has a large number of trapping states as attributed to the cadmium-related vacancy and Ga-impurity, diffused from the substrate, related defect complexes.  相似文献   

7.
Growth characteristics of (100) HgCdTe (MCT) layers by MOVPE at low temperature of 275°C were studied using ditertiarybutyltelluride as a tellurium precursor. Growths were conducted in a vertical narrow-spacing growth cell at atmospheric pressure. Cd composition of MCT layers were controlled from 0 to 0.98 using dimethylcadmium (DMCd) flow. The growth rate was constant for increase of DMCd flow. During the growth, Cd was incorporated preferentially into the MCT layers. Enhancement of Cd incorporation in the presence of Hg was also observed. Crystal quality and electrical properties were also evaluated, which showed that high quality MCT layers can be grown at 275°C. Strain in CdTe layers grown at 425 and 275°C was also evaluated. Lattice parameter of layers grown at 425°C approached bulk value at thickness of 5 μm, while layers grown at 275°C relaxed at 1 μm. The rapid strain relaxation of layers grown at 275°C was considered due to the layer growth on the strain relaxed buffer layer. The effect of the thermal stress on the relaxation of CdTe lattice strain was also discussed.  相似文献   

8.
Growth characteristics of (100)-oriented CdZnTe layers grown by atmospheric-pressure metalorganic vapor phase epitaxy have been studied using dimethylzinc (DMZn), dimethylcadmium (DMCd), diethyltelluride (DETe), and dimethyltelluride (DMTe) as precursors. Variations of Zn composition and layer growth rate were examined by changing the DMZn supply ratio, defined as DMZn/(DMCd+DMZn), where the precursors are expressed in appropriate units of flow rate, from 0 (no DMZn) to 1.0 (no DMCd), while keeping the total group II supply rate constant. The growth rate of CdZnTe layers was found to decrease monotonically with increase of the DMZn supply ratio. On the other hand, the Zn composition x of grown layers increased gradually up to x=0.04 with increase of the DMZn supply ratio from 0 to 0.8, beyond which the Zn composition increased abruptly to ZnTe. The abrupt transition of Zn composition was suppressed by increasing the VI/II ratio. The growth mechanism of CdZnTe layers was studied based on the observed growth characteristics of CdTe and ZnTe. A higher desorption rate from the growth surface for Zn species than for Cd species, and a higher rate of CdTe formation than ZnTe formation are believed to cause the observed growth characteristics. CdZnTe layers with high crystal quality were grown in a wide range of Zn compositions. The full-width at half-maximum values for x-ray double-crystal rocking-curve measurements were lower than 320 arc-sec for x<0.3 and x>0.75.  相似文献   

9.
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 (Ix) 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.  相似文献   

10.
Direct growth of high-quality, thick CdTe (211) epilayers, with thickness up to 100 μm, on Si (211) substrates in a vertical metalorganic vapor phase epitaxy system is reported. In order to obtain homo-orientation growth on Si substrates, pretreatment of the substrates was carried out in a separate chamber by annealing them together with pieces of GaAs at 800–900°C in a hydrogen environment. Grown epilayers had very good substrate adhesion. The full-width at half-maximum (FWHM) value of the x-ray double-crystal rocking curve from the CdTe (422) reflection decreased rapidly with increasing layer thickness and remained between 140–200 arcsec for layers >18 μm. Photoluminescence measurement at 4.2 K showed high-intensity, bound excitonic emission and very small defect-related deep emissions, indicating the high crystalline quality of the grown layers. Furthermore, a CdTe/n+-Si heterojunction diode was fabricated that exhibited clear rectifying behavior.  相似文献   

11.
Growth characteristics of (100) Cd1−xZnxTe (CZT) have been studied using metalorganic vapor phase epitaxy. CZT layers were grown on (100) GaAs substrates using diisopropylzinc (DiPZn), dimethylcadmiun (DMCd), and diethyltelluride (DETe) as precursors. Growths were carried out in the temperature range from 375 to 450°C. Since DiPZn has lower vapor pressure than DMCd, CZT layers with Zn composition below 0.06 were grown with good compositional control. Layers with uniform Zn composition and thickness over an area of 10 × 15 mm2 were grown. Enhancement of CZT growth rate was observed when a small amount of DiPZn is introduced under fixed flows of DMCd and DETe. Zn composition increases abruptly for further increase of DiPZn flow rate, where growth rate decreases. Growth mechanisms for the above growth conditions were also discussed.  相似文献   

12.
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.  相似文献   

13.
Carbon tetrabromide was used as carbon source for heavily p-doped GaAs in low pressure metalorganic vapor phase epitaxy (MOVPE). The efficiency of carbon incorporation was investigated at temperatures between 550 and 670°C, at V/III ratios from 1 to 50 and carbon tetrabromide partial pressures from 0.01 to 0.03 Pa. Hole concentrations from 8 × 1017 to 5 × 1019 cm−3 in as-grown layers were obtained. After annealing in nitrogen atmosphere at 450°C, a maximum hole concentration of 9 × 1019 cm−3 and a mobility of 87 cm2/Vs was found. At growth temperatures below 600°C, traces of bromine were detected in the layers. Photoluminescence mapping revealed an excellent doping homogeneity. Thus, CBr4 is found to be a suitable carbon dopant source in MOVPE.  相似文献   

14.
The growth characteristics and crystalline quality of thick (100) CdTe-epitaxial layers grown on (100) GaAs and (100) GaAs/Si substrates in a metal-organic vapor-phase epitaxy (MOVPE) system for possible applications in x-ray imaging detectors were investigated. High-crystalline-quality epitaxial layers of thickness greater than 100 μm could be readily obtained on both types of substrates. The full width at half maximum (FWHM) values of the x-ray double-crystal rocking curve (DCRC) decreased rapidly with increasing layer thickness, and remained around 50–70 arcsec for layers thicker than 30 μm on both types of substrates. Photoluminescence (PL) measurement showed high-intensity excitonic emission with very small defect-related peaks from both types of epilayers. Stress analysis carried out by performing PL as a function of layer thickness showed the layers were strained and a small amount of residual stress, compressive in CdTe/GaAs and tensile in CdTe/GaAs/Si, remained even in the thick layers. Furthermore, the resistivity of the layers on the GaAs substrate was found to be lower than that of layers on GaAs/Si possibly because of the difference of the activation of incorporated impurity from the substrates because of the different kinds of stress existing on them. A heterojunction diode was then fabricated by growing a CdTe epilayer on an n+-GaAs substrate, which exhibited a good rectification property with a low value of reverse-bias leakage current even at high applied biases.  相似文献   

15.
6H-SiC/GaN pn-heterostructures were grown by subsequent epitaxial growth of p-SiC by low temperature liquid phase epitaxy (LTLPE) and n-GaN by hydride vapor phase epitaxy (HVPE). For the first time, p-type epitaxial layers grown on 6H-SiC wafers were used as substrates for GaN HVPE growth. The GaN layers exhibit high crystal quality which was determined by x-ray diffraction. The full width at a half maximum (FWHM) for the ω-scan rocking curve for (0002) GaN reflection was ∼120 arcsec. The photoluminescence spectra for these films were dominated by band-edge emission. The FWHM of the edge PL peak at 361 nm was about 5 nm (80K).  相似文献   

16.
The focus of this paper is the integrated use of system and wafer monitors to obtain a complete picture of the growth process and to identify the major causes of variance. In situ monitoring of a growing layer of Hg1-xCdxTe using laser reflectometry has been compared with the outputs of various system monitors such as pyrometer, organometallic concentration, and flow. Differences between the expected and measured concentrations were corrected by initially adjusting the organometallic flows, and the remaining variance in CdTe interdiffused multilayer process layer thickness was then corrected by increasing the CdTe cycle time. The remainder of the layer gave a homogenized alloy composition of 0.256 for a target value of 0.258. This example shows how different in situ monitors have been integrated to give a comprehensive picture of the growth process, which were then related to known kinetic behavior. As a result of this monitoring, it was possible to identify critical parameters for control.  相似文献   

17.
Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, xBi, lower than 0.2 at.%, an excess deep-donor level (activation energy Ed≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for xBi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 1017 cm−3. Inductive coupled plasma (ICP) emission analysis shows that, for xBi=1 at.%, Bi concentration in the epitaxial layer is as high as NBi=2.3–2.7 × 1019 cm−3. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10−5 torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.  相似文献   

18.
In this study, the use of a novel phosphorous precursor for low pressure metalorganic vapor phase epitaxy (LP-MOVPE) application has been investigated. Ditertiarybutyl phosphine ((C4H9)2-P-H, DitBuPH) as substitute for the standardly used hydrid gas phosphine (PH3) promises apart from strongly reduced toxicity due to the reduction of P-H bonds, an enhancement in cracking efficiency as well as a reduction in growth temperature. Layer quality has been examined by means of optical and scanning electron microscopy (SEM), temperature-dependent van der Pauw Hall as well as photoluminescence (PL) measurements. Uncompensated n-type InP-layers (1.0 x 1.5 cm-3; 59600 cm2Vs)-1 at 77K) are realized using DitBuPH in combination with commercial TMIn. All results are compared with those obtained by using PH3 and commercial tertiarybutyl phosphine (TBP) as P-source, respectively.  相似文献   

19.
Biaxial tensile strain is introduced into (AlP)n(GaP)n superlattices (SLs) by growing the SLs on slightly lattice-mismatched InGaP intermediate layers on GaP(00l) substrates. A significant enhancement of photoluminescence intensity is observed for the strained (AlP)n (GaP)n short-period SLs, especially for those with n≤ 3.  相似文献   

20.
ZnSySe1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSyySe1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is hc ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnSySe1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnSySe1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.  相似文献   

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