Akikazu Tanaka

Zinc and selenium co-doped CdTe substrates lattice matched to HgCdTe

Abstract A CdTe crystal co-doped with zinc and selenium was grown by the gradient freeze method to obtain substrate material which is lattice matched to HgCdTe. After the measurement of the segregation coefficient of each dopant, a charge composition was estimated to realize a uniform and suitable lattice constant. The crystal grown from the charge exhibited not only a very uniform lattice constant within the range of fraction solidified between 0 and 0.7, but also high crystal perfection as indicated by low dislocation density (3×10 3 cm −2 ) and high infrared transmission (>62%). CdTe doped with Zn and Se is therefore a very promising material as a substrate of HgCdTe epitaxial growth.

Chlorine-related photoluminescence lines in high-resistivity Cl-doped CdTe

Abstract High-resistivity Cl-doped CdTe crystals grown by the gradient-freeze method were studied by high-resolution photoluminescence (PL) and electrical measurements. A sharp PL line ascribed to a Cl-related defect was observed at 1.5903 eV in all of the high-resistivity crystals doped with different amounts of chlorine. A broad line around 1.586 eV was clearly observed in highly doped crystals. The intensities of these lines increased with the amount of chlorine. Annealing under Cd-saturated atmosphere eliminated the 1.5903 eV line and intensified the neutral donor-bound exciton line together with its two-electron transition. The high-resistivity crystals were also converted to n-type with low resistivity by the Cd annealing. These results show that the 1.5903 eV line is a key emission line for the high-resistivity, and suggest that the line is associated with Cd-vacancy/chlorine complex, probably in the form of V CD -Cl.

Carrier drift mobilities and PL spectra of high resistivity Cadmium Telluride

Abstract Time-of-flight (TOF) measurements and photoluminescence (PL) properties of Cl-doped semi-insulating CdTe, grown by the gradient freeze (GF) method are described. By choosing appropriate growth conditions, drift mobilities as high as 1100 and 80 cm 2 /V·s for electrons and holes respectively were obtained, which are comparable to those grown by the traveling heater method (THM). From a comparison of PL and TOF results, correlations between the intensity of PL line W (at 1.587 eV) and the drift mobilities of both electrons and holes have been found. The relations of the PL lines W and G (at 1.591 eV) are analyzed by a compensating defect model composed of (V Cd Cl Te ) and (V Cd 2Cl Te ).

Annealing behavior of bound exciton lines in high quality CdTe

Annealing behavior of shallow donor‐bound and acceptor‐bound exciton lines in CdTe crystals grown by the Bridgman method was investigated by high‐resoluton photoluminescence measurements at 4.2 K. The intensity of the neutral acceptor‐bound exciton line (A0X) at 1.5896 eV, which was commonly observed in p‐type CdTe, drastically decreased by annealing under Cd saturated atmosphere. By further subsequent annealing under Te saturated atmosphere, the A0X line recovered again. On the other hand, the intensity of the neutral donor‐bound exciton line increased by annealing under Cd saturated atmosphere and decreased by the further annealing under Te saturated atmosphere. It was found that this change in the photoluminescence lines by the annealing process was reversible. These results strongly suggest that the A0X line at 1.5896 eV can be ascribed to the recombination of excitons trapped at Cd‐vacancy/donor‐impurity complexes.

Growth Characteristics and Electrical Properties of (100) CdTe Layers Grown on (100) GaAs by Low-Pressure Organometallic Vapor Phase Epitaxy

The growth mechanism and electrical characteristics of (100) CdTe layers grown on (100) GaAs by low-pressure organometallic vapor phase epitaxy have been reported. The growth mechanism changed around the growth temperature of 400°C. Adduct pyrolysis dominated the growth below the temperature of 400°C. Above this temperature, a pyrolysis of DETe dominated the growth. High-quality p-type layers were obtained when the layers were grown thicker than 2 µm at 420°C. The hole density and the Hall hole mobility were in the ranges of 2.2-3.5×1015 cm-3 and 60–100 cm2/V·s, respectively. In contrast to this, the grown layer became semi-insulating when the thickness was less than 2 µm due to out-diffusion of Ga from the substrates. The double crystal X-ray rocking curve also showed a FWHM value of 155 arcsec at the thickness of 6 µm.

Correlation between electrical and photoluminescence measurements in high‐quality p‐type CdTe

High‐quality p‐type CdTe crystals grown by the gradient freeze method were characterized by the radial resistivity distribution, Hall‐effect, and photoluminescence (PL) measurements. These measurements were performed over the crystal ingot as a function of position along the growth direction. The resistivity and the carrier concentration monotonically varied from 200 to 20 Ω cm and from 1×1014 to 1×1015 cm−3 along the growth direction, respectively. All photoluminescence spectra measured have well‐resolved spectra. It was found that both the resistivity and the carrier concentration strongly correlate to the photoluminescence intensity ratios of the neutral donor‐bound to the neutral acceptor‐bound exciton lines. The Hall mobility slightly decreased along the growth direction, and this result corresponded to the broadening of one longitudinal‐optic‐phonon replica of free excitons in the PL spectra. This good correspondence between the electrical properties and the PL spectra has provided useful means for ...

Photoluminescence and annealing behavior of Ga-doped CdTe crystals

Ga-doped CdTe crystals grown by the vertical gradient freeze method were studied by measuring high-resolution photoluminescence (PL) and electrical properties. Comparisons were made for as-grown and annealed samples under Cd saturation. The as-grown samples grown from slightly Te rich melt were of high resistivity (108 Ω cm) although gallium on the Te site alone in CdTe acts usually as a shallow donor. The Cd-annealed samples, on the other hand, were n-type with low resistivity. A new prominent PL line at 1.5841 eV was found in the high-resistivity as-grown crystals. Furthermore, the 1.5841 eV line completely disappeared after Cd annealing. These results suggest that the luminescence center related to the 1.5841 eV line is a Cd-vacancy/gallium associated and is responsible for high resistivity. This is direct evidence to explain the high-resistivity mechanism due to so-called self-compensation in CdTe(Ga). The two-electron transitions in Ga donors measured by PL are also reported.

X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses of the initial growth mechanism of CdTe layers on (100) GaAs by metalorganic vapor phase epitaxy

X‐ray photoelectron spectroscopy and Auger electron spectroscopy measurements were performed to investigate the initial growth mechanism and the selection of growth orientations of CdTe layers grown on (100) GaAs by metalorganic vapor phase epitaxy (MOVPE). The surface stoichiometry of the GaAs substrate was found to recover when annealed in a H2 flow atmosphere (500 °C, 5 min), although the surface was initially in an As‐rich condition after chemical etching by H2SO4: H2O2: H2O=5: 1: 1. No oxide was observed at both the etched and H2 annealed GaAs surfaces. Preferential adsorption of Te occurred on the GaAs surface when H2 annealing was carried out in the growth reactor in the presence of residual CdTe deposits. One monolayer of Te with a thickness of about 1.8 A was adsorbed on the GaAs surface when the H2 annealed GaAs was exposed to diethyltelluride during the cooling period from the annealing temperature to the growth temperature (420 °C). On the other hand, minimal adsorption of Cd occurred when the...

Mechanism of arsenic incorporation and electrical properties in CdTe layers grown by metalorganic vapor phase epitaxy

The As doping mechanism in (100) CdTe layers grown on (100) GaAs by atmospheric‐pressure metalorganic vapor phase epitaxy was studied. Triethylarsine (TEAs) was used as a dopant source. The source materials used were dimethylcadmium (DMCd) and diethyltelluride (DETe). The As incorporation was enhanced by decreasing the DETe flow rate under a fixed DMCd flow condition, and by lowering the growth temperature. Assuming 100% activation of As, the As incorporation efficiency was estimated to be about 0.1%. The As incorporation was dominated by the sticking rate of the As species onto the Cd species. The hole concentration was controlled from 2×1015 to 3×1016 cm−3 in proportion to the TEAs flow rate below 1×10−7 mol/min. Those doped layers showed hole mobilities as high as 75 cm2/V s. Low‐temperature photoluminescence (PL) studies revealed that a neutral‐acceptor bound‐exciton at 1.5901 eV is due to a substitutional As acceptor on the Te site. The As ionization energy was about 90 meV from the PL and electrical...

X‐ray photoelectron spectroscopy studies of initial growth mechanism of CdTe layers grown on (100)GaAs by organometallic vapor phase epitaxy

Variations of the GaAs surface conditions and the adsorption of the precursor elements of Cd and Te on the (100)GaAs substrate were studied by x‐ray photoelectron spectroscopy at the initial stage of CdTe growth by organometallic vapor phase epitaxy. The stoichiometry of GaAs substrates was found to recover by annealing in the H2 environment (500 °C, 5 min), while the surface was initially in an As‐rich condition after etching with H2SO4:H2O2:H2O (5:1:1). The preferential adsorption of Te on the GaAs surface was also observed. 〈100〉 oriented growth was obtained routinely when the GaAs surface was fully stabilized with Te after the H2 anneal under the above conditions. 〈111〉 oriented growth resulted when dimethylcadmium was first introduced after the anneal.