Kazuki Hayashida

Photoluminescence of iodine-doped ZnTe homoepitaxial layer grown by metalorganic vapor phase epitaxy

Photoluminescence (PL) properties of I-doped ZnTe homoepitaxial layers grown by atmospheric pressure metalorganic vapor phase epitaxy have been investigated as a function of n-butyliodide (n-BuI) transport rate. The PL spectrum changed drastically even when a low dopant transport rate was used. A structured emission band at 2.22 eV was detected predominantly at low n-BuI transport rates, whereas a structureless broad emission band at around 2.17 eV or less dominates the PL spectrum at high n-BuI transport rates. PL spectra of I-doped ZnTe layers were analyzed at varying excitation power and temperature. These luminescence bands are due to donor–acceptor pair recombination, and may be ascribed to complexes consisting of Zn vacancies and I on Te sites close to donors.

Photoluminescence of Cl-doped ZnTe epitaxial layer grown by atmospheric pressure metalorganic vapor phase epitaxy

Effects of Cl doping on the photoluminescence (PL) of ZnTe homoepitaxial layers grown by atmospheric pressure metalorganic vapor phase epitaxy using n-butylchloride (n-BuCl) have been investigated. A quite strong donor bound excitonic emission was observed by increasing the n-BuCl transport rate, implying that Cl is incorporated into ZnTe layer as a donor. From the temperature dependence of PL spectra, the thermal activation energy of donor bound excitonic emission was found to be 5.9 meV. Two luminescence bands due to donor-acceptor pair emission appeared at 2.34 and 2.22 eV in the layer grown at an n-BuCl transport rate as high as 0.2 μmol/min. The donor and acceptor levels corresponding to the PL peak at 2.34 eV were estimated to be 22 and 51 meV from the excitation power dependence of PL peak energy, respectively.

Effect of VI/II ratio upon photoluminescence properties of aluminum-doped ZnTe layers grown by MOVPE

Abstract The photoluminescence properties of aluminum (Al)-doped ZnTe layers grown by atmospheric pressure metalorganic vapor phase epitaxy have been investigated as a function of the ratio of transport rate of diethyltelluride and dimethyl (VI/II ratio). When VI/II ratio is increased, the excitonic emission and donor–acceptor pair emission due to Al donor become predominantly in the spectrum of ZnTe layer. This suggests that Al is effectively incorporated into ZnTe. Several bound excitonic emissions associated with residual acceptor impurities are also detected in the spectrum together with free excitonic emission. When VI/II ratio exceeds 3, the deep level emission associated with the complex of Al donor and Zn vacancy which roles the acceptor for ZnTe are induced. It seems that the intensity of this emission band is independent of dopant transport rate.

Photoluminescence properties of ZnTe homoepitaxial layers grown by synchrotron-radiation-excited growth using nitrogen carrier gas

Abstract ZnTe homoepitaxial layers have been grown by synchrotron-radiation-excited growth using diethylzinc and diethyltelluride with nitrogen carrier gas. Effects of carrier gas on the growth rate and photoluminescence (PL) properties of the ZnTe layers have been investigated. No remarkable difference was found in the growth rate of the deposited layer between hydrogen and nitrogen carrier gases at low substrate temperature up to 60 °C. However, at high substrate temperature, the growth rate obtained using nitrogen carrier gas exhibits only a slight reduction, while that using hydrogen is significantly reduced. PL spectra exhibit a sharp excitonic emission at 2.375 eV associated with shallow acceptor in the ZnTe layer grown under the condition of various VI/II ratios and substrate temperature condition by using nitrogen carrier gas, different from the case of hydrogen carrier gas.

Design of Beamline BL9 at Saga Light Source

Saga Light Source (SAGA‐LS), which has been constructed at Tosu city in Saga prefecture, is a compact synchrotron light source with storage electron energy of 1.4 GeV. A new beamline for the development of advanced materials and processing has been designed, and is now under construction at BL9 of SAGA‐LS. This beamline is one of the three bending magnet beamlines (BL9, BL12, and BL15) constructed by Saga Prefectural Government. In this paper, we describe the design and the expected optical performance of the beamline BL9 at SAGA‐LS.

Synchrotron Radiation‐Excited Etching of ZnTe

Synchrotron radiation‐excited etching of compound semiconductor, ZnTe, was investigated using the SF6 and Ar gases. In the case of SF6 gas, the ZnTe was not etched but thin film of a fluorine containing material, e.g. ZnF2, was deposited on the surface of ZnTe. On the other hand, ZnTe was etched by using Ar gas under the negative sample bias to the sample. The etched pattern obtained by placing a Ni mesh showed that only the irradiated area was etched. The etching rate was estimated to be around 4.5×10−2 A/mA⋅min.

Growth of n-type ZnTe films and formation of ohmic contacts

N-type ZnTe films with resistivities of 2 and 13 (Omega) cm have been grown by metalorganic vapor phase epitaxial technique using triethylaluminum. The photoluminescence spectra from these films exhibit strong excitonic emission and donor-acceptor-pair emission associated with Al donor and very weak deep emission band due to the Zn vacancy and Al donor complex. We have examined various metals (Al, Mg and W) and an alloy (In-Hg) for ohmic contacts to n-type ZnTe. From the current-voltage characteristics between two contacts at room temperature for above-mentioned metals and alloy, it has been found that acceptable contacts are formed using W and In-Hg alloy. The best contact among the investigated electrodes is achievable by using W electrode.

Recent studies on metalorganic vapor phase epitaxial growth of ZnTe

Results of our recent experiments relating to ZnTe homoepitaxial growth by atmospheric pressure metalorganic vapor phase epitaxy are described. The effects of substrate temperature, gas flow rate and VI/II ratio upon the growth rate of ZnTe layers have been investigated. The behavior of the growth rate is well explained with a simplified growth model, in which the diffusion in the boundary layer and the reaction-rate law described by Langmuir-Hinshelwood model are considered. We also deal with the results on the photoluminescence properties of ZnTe layers obtained under wide growth conditions covered from mass transport limited region to kinetically controlled one. The growth conditions close to the transition part between mass transport and surface kinetic regions led to ZnTe layer of high quality. Similar conclusion is also obtained for photo-assisted growth. Photo-assisted growth enlarges substrate temperature range for achieving ZnTe layer of good quality compared with thermal growth.

Recent studies on ZnTe homoepitaxial films deposited by synchrotron-radiation-excited growth

Results of our recent experiments relating to the synchrotron-radiation (SR)-excited growth of ZnTe on the (100) ZnTe substrate using metalorganic sources are described. We have clarified the growth characteristics and quality of ZnTe films. The shape of deposited film suggests that surface excitation process, i.e., the excitation of the adsorbed species or sample surface, will be the dominant mechanism. The quantum yield for forming ZnTe molecules was estimated to be as high as 0.3% in the room temperature growth. ZnTe epitaxial film without carbon and oxygen contamination is attainable even at room temperature using SR as a light source. Near band gap luminescence can be observed even in the films grown at room temperature. It seems that a use of N2 carrier gas is promising for the inclusion of nitrogen as shallow acceptors and the suppression of defects. Through these experiments, we propose that the SR-excited growth is a powerful technique for a novel low temperature growth of compounds.