Atsushi Kamata

Superiority of group VII elements over group III elements as donor dopants in MOCVD ZnSe

Abstract Comparison of group III and group VII elements as donor species in ZnSe MOCVD growth has been studied from the viewpoint of their electrical properties, luminescence qualities and their controllabilities. Low resistivity high quality blue emitting ZnSe has been grown by doping a group VII donor chlorine, in atmospheric MOCVD. The superiority of group VII elements over group III elements with regard to carrier concentration controllability and carrier producing efficiency has been predicted.

Characterization of ZnSSe on GaAs by etching and X-ray diffraction

Abstract Zinc sulfoselenide epitaxial layers grown on GaAs substrates have been characterized by etch pit density (EPD) and full width at half maximum (FWHM) of double-crystal X-ray rocking curves. EPD was observed on a (100) ZnS x Se 1- x /GaAs surface. The etching solution of 0.04% bromine-methanol at 3°C was found to work well for EPD measurement. EPD on the ZnSe epilayers was about 10 7 cm -2 for the general growth conditions, but was as low as 10 4 cm -2 for lattice-matched ZnS x Se 1- x epitaxial layers which gave the narrowest FWHM of 13.6 arc sec.

Undoped ZnSe single crystal growth by the vertical Bridgman method

Abstract We have successfully grown twin free undoped ZnSe crystals by the vertical Bridgman method. The single crystals were as large as 25 mm in diameter by 25 mm in length. The macro-defects, such as voids and twins, were reduced drastically by selecting the downward velocity of the crucible and the angle of the crucible cone. Large twin free crystals were obtained when the velocity was not more than 4 mm/h and the crucible cone angle was either 30° or 45°. For crucible velocities greater than 4 mm/h, only polycrystalline material was obtained. In high purity ingots, the concentrations of various impurities were found to be either less than 1 ppm or under the detection limit.

The zinc pressure effect in chlorine-doped ZnSe grown by atmospheric metalorganic chemical vapor deposition

An n‐type ZnSe has been grown by atmospheric metalorganic chemical vapor deposition in which hydrogen chloride was used as the chlorine‐donor source. Epitaxial layers were evaluated by photoluminescence measurements and Hall measurements. An excitonic emission intensity at 4.2 K, which is a donor bound excitonic emission, increased with donor doping concentration increase. The electron carrier concentration varied with a quadratic dependence on the dopant concentration. Chlorine‐doped ZnSe characteristics were revealed to be similar in regard to the relation between the electrical and luminescent properties, irrespective of dopant source materials. An increase in zinc partial pressure led to an increase in carrier concentration and the suppression of the self‐activated emission intensity. A zinc excess growth condition was revealed to be effective for quality improvement for n‐type ZnSe and suppression of the compensation effect, which made the carrier producing efficiency high.

p-type carrier concentration control in lithium-doped zinc selenide grown by MOCVD

Abstract Lithium-doped ZnSe epitaxial layers have been grown on GaAs substrates by metalorganic chemical vapor deposition. Tert-butyllithium (TBL) was used as a doping material. Secondary ion mass spectroscopy showed that Li concentrations in ZnSe layers could be altered from 4×10 17 to 4×10 17 cm -3 by variation of the carrier gas flow rate passing through the TBL cylinder. Photoluminescence measured at 4.2 K indicated acceptor concentration increased with TBL carrier gas flow rate. Carrier concentrations N A − N D obtained from C − V measurements increased to about 1×10 15 cm -3 with increasing TBL carrier flow rate.

Growth and doping characteristics of ZnSeTe epilayers by MOCVD

Abstract Compositional control, band gap evaluation and acceptor doping characterization for ZnSeTe have been studied. Zinc selenotelluride layers were grown on GaAs (100) substrates by atmospheric metalorganic chemical vapor deposition. The composition of the ZnSexTe(1−x) solid is proportional to the gas phase composition when the VI II ratio is close to unity. Accurate band gap energy values for ZnSeTe epilayers were obtained at room temperature by photoreflectance spectroscopy. The bowing parameter is 1.647 eV. The p-type carrier concentration of ZnSeTe:As is drastically quenched with increasing Se incorporation. The quenching is possibly attributable to the lattice distortion.

Highly Conductive P-Type ZnTe:As Grown by Atmospheric Metalorganic Chemical Vapor Deposition Using Trimethylarsine

Highly conductive p-type ZnTe was grown by atmospheric metalorganic chemical vapor deposition (MOCVD). The source materials were dimethylzinc and diisopropyltelluride. Arsenic was doped into ZnTe with trimethylarsine. The carrier concentration depended on both the growth temperature and VI/II ratio. The highest carrier concentration measured in Hall measurements was 1.3×1019 cm-3, which is the highest ever reported for MOCVD-grown ZnTe. Low-temperature photoluminescence spectra showed strong As-related bound exciton lines and donor-to-acceptor recombination lines.

Novel nitrogen source materials in zinc selenide metalorganic chemical vapor deposition

Abstract Novel nitrogen-based materials have been used as nitrogen sources in metalorganic chemical vapor deposition (MOCVD) grown ZnSe. Ethylazide has a high doping efficiency and the controllability of the doping concentration is good. Photoluminescence spectra at 4.2 K revealed the presence of shallow acceptor levels in ZnSe. Hydrogen was incorporated into the ZnSe layer at a similar concentration of that of nitrogen, although the nitrogen-hydrogen bond did not exist in ethylazide. The high resistivity of the present samples was due to the hydrogen passivation. The formation of the N-H bond should be prevented in the growth atmosphere.

Raman spectra of CuAlSe2 heteroepitaxial layers

Room‐temperature Raman spectra were measured for CuAlSe2 heteroepitaxial layers grown on GaAs (001) and GaP (001) substrates. A remarkable difference in the polarized Raman spectra was noted, and the results were attributed to be due to the lattice orientation of the epilayers on the basis of the polarization selection rules of Raman active modes. Two vibrational modes were assigned, namely the A1 mode at 189 cm−1 and longitudinal‐optical B2 mode at 89 cm−1.

CdZnSe-ZnSe multilayers by metalorganic vapour phase epitaxy using dimethylselenide

The growth of CdZnSe-ZnSe multilayers using (CH 3 ) 2 Se at 475 o C is reported. Despite the occurrence of thermally induced diffusion, observed by secondary ion mass spectrometry, quantum wells of the desired alloy composition have been successfully grown for a well width of 20 nm. The uniform layers which can be obtained using dimethylselenide as the group VI precursor allow stimulated emission to be observed at 77 K from a multiple quantum well structure consisting of three, 30 nm wells under nitrogen laser excitation