Yoshimasa Ohki

Selective Area Epitaxy of GaAs Using GaAs Oxide as a Mask

The use of GaAs oxide as a mask material for in situ selective-area epitaxy of GaAs by metal organic molecular beam epitaxy (MOMBE) was studied. The GaAs oxide mask was patterned by electron-beam-induced chlorine etching. Using trimethylgallium (TMG) and As4 as source materials, an epitaxial layer of GaAs was obtained on the opening of the GaAs oxide mask; no deposition was observed on the GaAs oxide. An observation of the thermal decomposition of TMG by mass spectrometry indicated that the thermal decomposition of TMG occurred above 350°C on an arsenic-stabilized surface, while decomposition did not occur below 550°C on the GaAs oxide surface. This surface-catalyzed reaction explains the selectivity of GaAs growth.

Analysis of GaAs MOMBE Reactions by Mass Spectrometry

The thermal decomposition of trimethylgallium (TMG) under metal-organic molecular beam epitaxy (MOMBE) conditions is studied by mass spectrometry. For the first time, it is observed that the amount of Ga-containing species desorbed from the GaAs surface decreases above 350°C. Measurements on CH3, CH4 and C2H6 indicate that TMG pyrolyzes by releasing methyl radicals. The amount of Ga-containing species desorbed from the SiO2 surface does not show a steep decrease up to 530°C, which indicates that no thermal decomposition occurs on SiO2. This explains the mechanism of selective epitaxy in MOMBE.

Pattern etching and selective growth of GaAs by in-situ electron-beam lithography using an oxidized thin layer

Pattern etching of GaAs by in situ electron-beam (EB) lithography using an oxidized thin ayer is performed in a multichamber system comprising seven chambers for loading sample exchange sample pre-heating molecular beam epitaxy (MBE) surface treatment etching and surface analysis. The in situ EB lithography process comprises the following steps using the multichamber system: (1 ) preparation of a clean GaAs surface by MBE (2) formation of GaAs oxide as a resist film by photo-oxidation in pure oxygen gas (3) direct patterning of the oxide resist film by EB-induced Cl2 etching (4) 012 gas etching of the GaAs surface as a pattern transfer and (5) removal of residual GaAs oxide layer by heating the wafer above about 600 00 in a vacuum under a partial pressure of arsenic. Overgrowth of GaAs and/or AIGaAs layers is also possible on a patterned GaAs wafer without exposing the surface to air. Damage to the patterned area was evaluated through photoluminescnece measurements and compared with the case of conventional dry etching of GaAs. The results showed that damage was extremely small for EB-induced Cl2 etching. The reason is considered to be due to a difference in momentum transfer from charged particles to the lattice. Selective-area epitaxy using this GaAs oxide layer as a mask film was carried out by combination of EB-induced Cl2 etching and metal organic molecular beam epitaxy (MOMBE) using a separate ultra-high

Temperature Dependence of the Reflected Trimethylgallium Flux Intensity from a GaAs Surface in Metal-Organic Molecular Beam Epitaxy Measured by Mass Spectrometry

Desorbed species from a substrate in metal-organic molecular beam epitaxy of GaAs using trimethylgallium (TMG) and As4 were studied by mass spectrometry. The observed Ga-containing species were mainly reflected TMG at all substrate temperatures ranging from 290 to 650°C. The TMG reflection decreased with an increase in the substrate temperature up to 520°C, indicating a decomposition of TMG on the GaAs surface. Above 520°C, the reflection of TMG increased and showed a small maximum at about 600°C. The temperature dependence of the reflected TMG accounts for the reported anomalous temperature dependence of the growth rate of GaAs by MOMBE.

Electric field-induced absorption in GaInAsP/InP MQW structures grown by LPE

The absorption spectrum induced by applying an electric field was measured for GaInAsP/InP MQW structures with the corresponding bandgap wavelength λg~1.3 µm. A 25-pairs MQW wafer was grown by LPE technique with a well width Lz=150 A, and a barrier width Lb=200 A. The maximum electro-absorption in this waveguide structure was observed to be 550 cm-1 at an applied voltage of 25 V. From this value, the refractive index variation in the quantum well layer was estimated as 0.27%.

Epitaxy and Pattern Formation of III- V Semiconductors as a Through UHV Processing towards 2- and 3-Dimensional Nanostructures

There has been a growing interest in 2and/or 3 -dimensional seiniconductor heterostructures in the nanometer scale for future electronic and optoelectronic devices.l) To fabricate such nanostructures, a through ultra-high vacuum (UHV) processing of III-V semiconductors where the epitaxy and the pattern etching are performed successively without unintentional surf ace contamination caused by air exposure is regarded as a most probable candidate.2,3) In this context, research concerning in situ patterning using focused-ion beam (FIB) has been carried out.4-6) However, in the processing using ion beam, it turned out that inherent drawback such as the ioninduced damage which extends deeply into the sample remains.7,8 ) We have recently reported a lithography process named in situ electron-beam (EB) lithography which is compatible with a through UHV processing of GaAs/AlGaAs system.g I 1 ) In in situ EB lithography, an ultrathin oxide of GaAs is used as both the resist film and the etching mask, which can be patterned by EB -induced CIZ etching, and can be removed by heating. In addition to in situ s-c-6

Effect of Arsenic Flux on Desorption of Methylgallium from GaAs Surface in Metal-Organic Molecular Beam Epitaxy Studied by Mass Spectrometry

Gallium-containing species desorbed from GaAs substrate surface were measured by mass spectromeEy under metalorganic molecular beam epitaxy conditions using trimethylgallium (TN{G) and arsenic 1As4) as source materials. The desorbed species were mainly TMG up to 600 oC under sufficient As4 flux. The methylgallium with one or two methyl groups desorbed above 400 oC under the As4 flux free condition. The epitaxial growttt of GaAs with alternating soruce supply mode, such as atomic layer epitaxy, contains a desorption process of methylgallium other ttran TMG during TMG was supplied.

Electric Field Induced Reflection in GaInAsP/InP MQW Structure

Reflection of light due to the electric field effect was seen for the first time in GaInAsP/InP MQW structures through the observation of an interference pattern between the transmitted and reflected light; this was caused by a change in the refractive index and absorption coefficient in the MQW layers due to the partial application of an electric field to the MQW layers. The observed data were fitted with the theoretical simulations and the refractive index change was predicted to be about 0.025% at -5 V. This is a promising step towards the realization of the intersectional optical switch.