Kohsuke Nishimura

Low temperature metalorganic vapor phase epitaxial growth of CdxZn1−xS on GaAs

Abstract A low temperature metalorganic vapor phase epitaxial growth of Cd x Zn 1− x S on a (100) GaAs substrate was demonstrated using tertiarybutylmercaptan (t-BuSH) as a sulfur source precursor. Three other organic sulfide source precursors were also examined for comparison. By using t-BuSH, high growth rate and good composition controllability were attained in the growth temperature range from 330 to 440°C. The epilayer grown at T g = 350° C without any buffer layer between the epilayer and the substrate showed excellent crystalline properties in a wide composition range 0.53≤ x ≤0.67. n-Type doping experiments using TEIn as a dopant source were also demonstrated and doped epilayers with maximum carrier concentration of 4×10 18 cm -3 were obtained.

High External Quantum Efficiency of Electroluminescence from Photoanodized Porous Silicon

Porous silicon (PS) light emitting diodes (LEDs) were fabricated from p+n Si wafers by photoanodization. The maximum external quantum efficiency (ηext) of electroluminescence (EL) from PS-LED up to 0.8%, which is the highest ever reported for PS-LEDs with solid state contact, was achieved under pulsed operation with 1% duty in ambient air. However, we found that PS-LED with a high ηext was accompanied by the problem of high series resistance.

Metalorganic Vapor Phase Epitaxy of ZnSe Using Tertiarybutylselenol as Selenium Source Precursor

Metalorganic vapor phase epitaxy of ZnSe on a GaAs substrate was carried out using a novel organic selenium source, tertiarybutylselenol (t-BuSeH), for the first time. A constant and high growth rate was attainable in the growth temperature range of 280-500°C using t-BuSeH. The low-temperature reaction between diethylzinc and t-BuSeH was virtually eliminated, therefore growth uniformity and reproducibility were satisfactory. The grown ZnSe layers were evaluated to be of high quality by photoluminescence and X-ray diffraction measurement.

Characterization of Layered Polysilane

Layered polysilane synthesized according to a new recipe was characterized mainly by photoluminescence (PL) measurement. The PL spectrum of the as-prepared sample had a broad peak at 2.0 eV. The PL peak of a sample annealed at 300°C was also at 2.0 eV, and its PL intensity was several times greater than that of the as-prepared sample. The PL peak of a sample annealed at 400°C was red-shifted and its PL intensity was lower than those of the others. On the other hand, the PL emission from a sample rinsed in HF solution was blue-shifted and had a little lower intensity. The interpretations of the experimental results are discussed.

Low temperature metalorganic vapor phase epitaxy of ZnSe and ZnSSe onto GaAs using tertiarybutylselenol

Abstract The metalorganic vapor phase epitaxy (MOVPE) growth of ZnSe using diethylzinc (DEZn) and tertiarybutylselenol (t-BuSeH) is described. The transition temperature from kinetically to diffusion controlled growth ( T t ) was as low as 280°C, which is the lowest value for the growth using organic selenium source precursor ever reported. The surface morphology was smoother for the layers grown at 300°C than those grown at higher temperatures. Free-excition emissions were observed for all the measured layers in 4.2 K photoluminescence (PL) spectra. However, the intensity of neutral-donor-bound exciton emissions were several times larger than that of free-exciton emissions for the layers grown at 300°C, which means there reside donor impurities in t-BuSeH. ZnSSe layers were also grown using tertiarybutylmercaptan (t-BuSH) as sulfur (S) source precursor. Although T t was 330°C for ZnS growth using DEZn and t-BuSH, the incorporation ratio of S was not drastically decreased as low as 300°C for ZnSSe due to pyrolysis enhancement by t-BuSeH.

Novel Structures for Porous Silicon Light-Emitting Diodes

In this paper, two novel structures of porous silicon (PS) light-emitting diodes (LEDs) are proposed aiming at the reduction of series resistance, Rs. The basic idea of the novel structures is to suppress the excessive growth of nanoporous silicon (nano-PS) layer that is electroluminescence- (EL-) active but highly resistive. The initial wafer of the first structure consists of a lightly-doped layer stacked on a highly-doped substrate. As a consequence of anodization, nano-PS layer is formed only in the lightly-doped layer, while meso-PS layer with moderate resistivity is formed in the highly-doped substrate. The second structure consists of alternately stacked nano- and meso-PS layers, since it is expected that multiple thin nano-PS layers connected in series are less resistive than a single thick nano-PS layer. Preliminary experimental results proved the effectiveness of these novel structures on the reduction of Rs.

Effects of Antimony Diffusion into Porous Silicon Light Emitting Diodes

Porous silicon (PS) light emitting diodes (LEDs) consisting of n-PS/p-PS/p-Si or n-PS/p-Si structures fabricated by postanodical Sb diffusion were characterized for assessment of the effect of Sb diffusion upon PS-LED characteristics. The homogeneity of electrical characteristics of PS-LEDs was improved by Sb diffusion. Consequently, the average series resistance of the Sb-diffused PS-LEDs was found to be lower than that of nondiffused PS-LEDs. The average external quantum efficiency of the PS-LEDs was also enhanced by Sb diffusion. The experimental results were discussed.

Thermal Diffusion of Antimony into Nanostructured Porous Silicon

The thermal diffusion of Sb was carried out from Sb-doped silicate glass into porous silicon (PS) layers. The depth profiles of diffused Sb in PS layers were fitted to complementary error function curves in order to estimate diffusion coefficients. It was found that diffusion coefficients of Sb in PS were larger and had lower activation energy than those of Sb in hydrogenated amorphous silicon (a-Si:H) for the temperature range investigated. The experimental results are discussed in relation to the diffusion mechanisms in a-Si:H.