Takuto Tsuji

Generation and suppression process of crystalline defects in GaP layers grown on misoriented Si(100) substrates

We have investigated the generation process of crystalline defects in GaP layers grown on Si substrates (GaP/Si) by molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). Transmission electron microscopy observations revealed that few threading defects such as stacking faults and threading dislocations are detected in GaP/Si by MEE. In addition, a regular network of misfit dislocations was generated during the lattice relaxation process. On the other hand, stacking faults were generated in high density at the hetero-interface and threading dislocations as well as interfacial misfit dislocations were observed in GaP/Si by MBE. The generation of stacking faults would be related to the coalescence or expansion of isolated GaP islands and the presence of stacking faults would affect the generation of threading dislocations.

Selective epitaxial growth of GaAs on Si with strained short-period superlattices by molecular beam epitaxy under atomic hydrogen irradiation

Selective epitaxial growth of GaAs on a Si substrate with (GaAs)m(GaP)n strained short-period superlattices (SSPSs) and GaP buffer layer was achieved by molecular beam epitaxy under atomic hydrogen irradiation. The selective epitaxial layers were grown two dimensionally so that reflection high-energy electron diffraction patterns maintained streaky patterns with no apparent transition to three-dimensional spot patterns during the selective epitaxial growth of the GaAs/SSPSs/GaP/Si structure. Therefore, generation of threading dislocations due to the three-dimensional island growth was suppressed, in spite of a large lattice mismatch. It was also confirmed that the thickness of each buffer layer was slightly increased near the edge of the masked region. Finally, the epitaxial patterns of GaAs clearly exhibit crystal facets.

Reduction of Point Defects and Formation of Abrupt Hetero-Interfaces in Low-Temperature Molecular Beam Epitaxy of GaAs and GaP under Atomic Hydrogen Irradiation.

The removal effect of excess As and P atoms adsorbed on GaAs (100) and GaP (100) surfaces by atomic hydrogen (H) irradiation was investigated by reflection high-energy electron diffraction and X-ray photoelectron spectroscopy. It was found that the excess As and P atoms were effectively removed by atomic H irradiation at a low temperature of 350°C. Then, we attempted to obtain a high-quality GaAs epitaxial layer and an ordered (GaAs)1(GaP)3 strained short-period superlattice (SSPS) with abrupt GaAs/GaP hetero-interfaces in the low-temperature growth under atomic H irradiation. The quality of the GaAs epitaxial layer and the abruptness of the GaAs/GaP hetero-interfaces in the (GaAs)1(GaP)3 SSPS were evaluated by photoluminescence, deep-level transient spectroscopy and transmission electron microscopy. As a result, it was clarified that the density of point defects in the GaAs epitaxial layer was reduced and an abrupt GaAs/GaP hetero-interface of the (GaAs)1(GaP)3 SSPS was formed in the low-temperature growth under atomic H irradiation.

Defect-Controlled Selective Epitaxial Growth of GaP on Si by Migration-Enhanced Epitaxy under Atomic Hydrogen Irradiation

We investigated the properties of deposition of GaP on dry-SiO2 and SiNx masks using molecular beam epitaxy (MBE) or migration-enhanced epitaxy (MEE) under atomic hydrogen irradiation and attempted the selective epitaxial growth of GaP-on-Si. The critical substrate temperature, below which poly-GaP was deposited on a mask layer, was lower for dry-SiO2 than that for SiNx, and was lowered by MEE rather than MBE. As a result, the selective epitaxial growth of GaP was achieved by MEE using the dry-SiO2 mask. It was found that the formation of large anti-phase domains expanding into the surface was suppressed by forming a P-prelayer at low temperature. It was also confirmed that the density of misfit dislocations at the GaP–Si hetero-interface was remarkably reduced with a decrease in the growth area.

Passivation of misfit dislocations by atomic hydrogen irradiation in lattice-mismatched heteroepitaxy

We investigated the passivation effect of misfit dislocations in an (InAs)1(GaAs)4 strained short-period superlattice grown on GaAs with atomic hydrogen (H) by transmission electron microscopy and electron-beam-induced current. The misfit dislocations in the 〈1 1 0〉 directions are generated at the heterointerface in order to accommodate the misfit strain. They were effectively passivated by atomic H irradiation during the growth and cooling processes. Furthermore, it was found that the misfit dislocation in the [1 1 0] direction was effectively passivated rather than that in the [1 1 0] direction. The desorption temperature of atomic H from the [1 1 0] misfit dislocation was higher than that from the [1 1 0] misfit dislocation. These phenomena could be attributed to the fact that the bonding strength of As-H is larger than that of GaH.

Reduction of threading dislocation density in an (InAs)1(GaAs)1 strained short-period superlattice by atomic hydrogen irradiation

The generation process of dislocations as well as the initial growth mechanism were investigated in the growth of an (InAs)1(GaAs)1 strained short-period superlattice (SSPS) on a GaAs (001) substrate under atomic hydrogen (H) irradiation. A two-dimensional (2D) growth mode was maintained even after lattice relaxation occurred for growth at 350° C. On the other hand, the growth mode changed from 2D to a three-dimensional (3D) one without atomic H irradiation. The threading dislocation density was remarkably reduced and the critical thickness was markedly increased by atomic H irradiation. Misfit dislocations propagating along the and directions were generated at the heterointerface. Such effects disappeared for growth at 500° C, where the atomic H atoms desorb from the growing surface. It was also found that 3D growth was more effectively suppressed in the growth of (InAs)1(GaAs)1 SSPS than in a In0.5Ga0.5As alloy which has the same average In composition as that of the SSPS.

Reduction of surface roughness of an AlAs/GaAs distributed Bragg reflector grown on Si with strained short-period superlattices

We fabricated an AlAs/GaAs distributed Bragg reflector (DBR) on Si substrates using multiple-strained short-period superlattices (SSPSs) and evaluated the surface roughness of the DBR. The surface roughness of the DBR was markedly reduced, compared with that of the DBR fabricated on GaAs directly grown on Si. The reduction of the surface roughness was enhanced by low growth temperature. These effects could be caused by the 2D growth in the growth of the DBR and SSPSs as well as the marked reduction of threading dislocations.

Application of an Educational Resource of Si Solar Cell Fabrication to the Return and Spread Program of the Result of Research by KAKENHI

1. はじめに これまでに我々は,シリコン(Si)太陽電池を作製 する実験教材を開発してきた.この実験教材は,実験 設備などで制限のある高等専門学校(高専)でも工学 実験に導入しやすいように,比較的整備しやすい電気 炉や蒸着装置などを使って,必要最低限の簡略化した 作製工程で Si 太陽電池を作製できる.そして,開発し た Si 太陽電池を作製する実験教材は,鈴鹿高専・電気 電子工学科の工学実験に導入し活用している .さら に,この実験教材は工学実験で活用するだけではなく, 中学生を含めた一般市民を対象とした公開講座にも応 用してきた . 一方,科学研究費助成事業(科研費)を手掛けてい る日本学術振興会は,科研費による研究成果の社会還 元,普及事業の推進を目的として「ひらめき☆ときめ きサイエンス〜ようこそ大学の研究室へ〜KAKENHI」を 実施している.この事業では,児童・生徒を対象とし て,若者の科学的好奇心を刺激して知的創造性を育む ことや,科研費による研究について,科学の興味深さ やおもしろさをわかりやすく発信することが求められ ており,我々が開発した Si 太陽電池を作製する教材は, この事業の趣旨に合致している.そこで本報告では, Si太陽電池作製教材のひらめき☆ときめきサイエンス への応用について報告する.

A simplified boron diffusion for preparing the silicon single crystal p-n junction as an educational device

The educational method which is including designing, making, and evaluating actual semiconductor devices with learning the theory is one of the best way to obtain the fundamental understanding of the device physics and to cultivate the ability to make unique ideas using the knowledge in the semiconductor device. In this paper, the simplified Boron thermal diffusion process using Sol-Gel material under normal air environment was proposed based on simple hypothesis and the feasibility of the reproducibility and reliability were investigated to simplify the diffusion process for making the educational devices, such as p-n junction, bipolar and pMOS devices. As the result, this method was successfully achieved making p+ region on the surface of the n-type silicon substrates with good reproducibility. And good rectification property of the p-n junctions was obtained successfully. This result indicates that there is a possibility to apply on the process making pMOS or bipolar transistors. It suggests that there...

Generation and Suppression of Stacking Faults in Gap Layers Grown on Si(100) Substrates by Molecular Beam Epitaxy and Migration Enhanced Epitaxy

We have investigated the generation process of crystalline defects in GaP layers grown on Si substrates (GaP/Si) by molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). Transmission electron microscopy observations revealed that a regular network of misfit dislocations was generated in GaP/Si by MEE. On the other hand, threading dislocations as well as interfacial misfit dislocations were observed in GaP/Si by MBE. Moreover, stacking faults were generated in high density at the hetero-interface of GaP/Si by MBE. The density of stacking faults was drastically reduced by MEE.