Yuji Hiratani

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.

In-situ selective-area epitaxy of a GaAs-based heterostructure using a GaAs oxide layer as a mask

Abstract The in-situ selective-area epitaxy of InGaAs/GaAs was demonstrated by combining a GaAs oxide mask with metalorganic molecular beam epitaxy (MOMBE). All of the necessary processes for selective-area epitaxy were carried out in a MOMBE system without exposing the wafer to air. A mass spectrometric analysis of the decomposition of the source materials indicates that the surface-catalyzed decomposition of the source materials induces selective growth.

In-situ selective-area epitaxy of GaAs using a GaAs oxide layer as a mask

Abstract Selective-area epitaxy of GaAs was performed by metalorganic molecular beam epitaxy using a GaAs oxide mask. No deposition of polycrystalline GaAs was observed on a GaAs oxide mask after the selective-area epitaxy using a trimethylgallium (TMG) and As 4 as source materials. An observation of the decomposition of TMG indicated that it occurred above 350°C on an oxide-free surface of GaAs, while decomposition did not occur below 550°C on a GaAs oxide surface. This surface-catalyzed decomposition of TMG explains the selectivity of GaAs growth.

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

Demonstration of Thermo-Optic Switch Consisting of Mach-Zehnder Polymer Waveguide Drawn Using Focused Proton Beam

We demonstrated a PMMA-based thermo-optic switch consisting of a Mach-Zehnder (MZ) type waveguide drawn by proton beam writing (PBW) and working at λ = 1.55 μm. The MZ waveguide was drawn by symmetrically coupling two Y junctions with a core width of 8 μm and a branching angle of 2°. A Ti thin-film heater and Al electrodes were formed on the surface of the MZ waveguide using conventional photolithography and wet-etching processes. An ON/OFF ratio of 9.0 dB and a switching power of 43.9 mW were obtained from the sample. The switching power is lower than for conventional commercial silica-based switches.

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.

Mach-Zehnder Type Thermo-Optic Switch with Antenna-Coupled Y-Junction Fabricated by Selective Photobleaching of Polysilane Films

The Mach-Zehnder type thermo-optic switch with antenna-coupled Y-junction was demonstrated for the first time. The selective photobleaching of the polysilane films are used for fabrication. The branching angle was 3 deg and the longitudinal length was around 30 mm, which was reduced as around 60 % from the conventional structure. The beam propagation method was used for optimizing the design and the calculated transmission loss was only 0.16 dB. Our experiments showed the ON/OFF ratio of 9.9 dB and the switching power of 11.4 mW.

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

Large difference in the decomposition rate of metalorganics between on As- and Ga-saturated GaAs (111)B surfaces

Abstract The termal decomposition of triethylgallium (TEG) on a GaAs (111)B surface was studied by mass spectrometry. The decomposition rate of TEG varies largely with the change of the surface As coverage; almost all of the TEG which impinged onto an As-saturated surface was reflected, while it decomposed swiftly on a Ga-saturated surface at temperatures ranging from 300 to 500°C. Above 400°C, a slight increase in the desorption of alkylgallium has accompanied the decomposition of TEG to Ga on Ga-saturated surface.

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.