Kenzo Akita

Composition dependence of the band gaps of In1−xGaxAs1−yPy quaternary solids lattice matched on InP substrates

The In‐Ga‐As‐P quaternary phase diagram required for the growth of lattice‐matched In1−xGaxAs1−yPy layers on InP substrates has been determined experimentally at 650 °C. The liquidus isotherms were obtained by the seed‐dissolution technique. The solidus iostherms were determined by electron‐microprobe analysis performed on surfaces of quaternary epitaxial layers grown on Sn‐doped InP (111) B substrates from quaternary saturated melts. Lattice constants of layers were measured by an x‐ray‐diffraction technique. The liquid‐phase‐epitaxy growth conditions of lattice‐matched In1−xGaxAs1−yPy (0⩽x⩽0.47, 0⩽y⩽1.0) layers on InP were found from the results of the phase diagram and lattice constant measurements. Lattice‐matched layers with various band gaps (from 1.34 to 0.74 eV at room temperature) were grown by using these conditions. Band gaps of the layers were determined by photoluminescence measurements at 300 and 77 K. The band gap at each temperature was found to be linearly dependent on alloy‐composition p...

Observation of etch pits produced in InP by new etchants

Abstract New etchants, HBr/HF or HBr/CH 3 COOH, produced sharp etch pits on (100) and (111) slices of InP. The etch pit shape produced on (100) by HBr/HF was pyramidal. The shape on (100) produced by HBr/CH 3 COOH varied from pyramidal to elongated rectangular along 〈110〉 with increasing the composition ratio of CH 3 COOH to HBr. The shape produced on (111)B by HBr/HF or HBr/CH 3 COOH was triangular pyramidal. The etch rates of these new etchants and HBr/H 3 PO 4 were measured as a function of composition ratio at room temperature. The correspondence between pits and dislocations was examined and the results indicated that etch pits produced by these etchants corresponded to dislocations.

Determination of In‐Ga‐As phase diagram at 650 °C and LPE growth of lattice‐matched In0.53Ga0.47As on InP

The liquidus isotherm in the In‐rich corner of the In‐Ga‐As system at 650 °C was experimentally determined by an improved seed dissolution technique using InP seeds. The solidus isotherms at this temperature were also determined in the composition range close to lattice‐matched In0.53Ga0.47As on InP. The solidus data are strongly affected by the crystallographic orientation of the substrate, but are not significantly affected by the degree of lattice matching. The calculated phase diagrams have been compared with the experimental results. The conditions for equilibrium LPE growth of exactly lattice‐matched ternary layers on InP (100) and (111) B substrates were obtained from the results of the phase diagram and lattice‐constant measurements. It was found that the distribution coefficient, growth rate, and surface morphology are strongly dependent on the substrate orientation. The distribution coefficient for Ga and the growth rate at 650 °C are both larger on the (100) face than on the (111) B face. Hillo...

Novel electron‐beam lithography for in situ patterning of GaAs using an oxidized surface thin layer as a resist

The first demonstration of in situ electron‐beam (EB) lithography is reported, where a photo‐oxidized surface thin layer of GaAs is used for a resist. The in situ EB lithography sequence consists of five processes, i.e., preparation of a clean GaAs surface, photo‐oxidation for a resist film formation, direct patterning of the oxide resist by EB‐induced Cl2 etching, Cl2 gas etching of GaAs surface for pattern transfer, and thermal treatment in an arsenic ambient for resist removal and surface cleaning. The GaAs wafer is never exposed to air throughout all of the above processes to avoid an unintentional surface contamination. The minimum electron dose required for patterning of the GaAs oxide resist is about 5×1016 cm−2. An overgrown layer on the patterned GaAs surface shows a good surface morphology, which strongly indicates that this technology makes it possible to repeat crystal growth and surface patterning.

Characterization of subsurface damage in GaAs processed by Ga+ focused ion‐beam‐assisted Cl2 etching using photoluminescence

Subsurface damage in GaAs processed by a Ga+ focused ion‐beam‐assisted Cl2 etching is studied by photoluminescence (PL) measurement. The PL intensity of the processed sample decreased to (1)/(30) – (1)/(40) compared to that of the unprocessed sample. The recovery of PL intensity by a step removal of the damaged layer is observed as a function of the removed layer thickness. The removal of a 0.7‐μm‐thick surface layer enables the PL intensity to be recovered perfectly, which leads to the postulate that the damaged layer thickness is 0.7 μm at least, which is much larger than the ion range (about 0.01 μm). The recovery of PL intensity is analyzed on a one‐dimensional model in the direction normal to the sample surface. Computer simulations of PL intensity are carried out. The calculated result fully explains the experimental PL intensity recovery as a function of the removed layer thickness, which gives the profile of subsurface damage in the sample.

Electron-Beam-Induced Cl2 Etching of GaAs

Electron-beam (EB)-induced Cl2 etching of GaAs is performed for the first time. Etching occurs only in the area exposed to both the Cl2 molecules and the EB. The etching rate is equal to that of a Cl2 gas phase etching. The morphologies of the etched surfaces are slightly rough, but the photoluminescence intensity of the processed sample does not change as compared with that of the unprocessed sample. The etching characteristics predict that surface adsorbates act as a mask for a gas phase etching and that the EB plays an important part in patterning of the adsorbate mask.

Misfit dislocation‐free In1−xGaxAs1−yPy/InP heterostructure wafers grown by liquid phase epitaxy

The conditions to grow misfit dislocation‐free In1−xGaxAs1−yPy/InP (0⩽x⩽0.47, 0⩽y⩽1.0) heterostructure wafers were first determined systematically by observing etch pits and x‐ray topographs. Etch pits were produced on InP substrates on which an In1−xGaxAs1−yPy layer was grown, and they were observed to find whether misfit dislocations generated or not. Threshold regions for initiation of misfit dislocations into the wafers were determined as a function of both lattice misfit and layer thickness. The misfit dislocation‐free regions determined by the etch pit observation of InP was found to be equivalent to the regions where misfit dislocations form in neither InP nor In1−xGaxAs1−yPy . The misfit dislocation‐free regions of the quaternary wafers are larger than the region of the ternary In1−xGaxAs/InP wafers by more than three times.

Misfit dislocations in InP/InGaAsP/InP double‐heterostructure wafers grown by liquid phase epitaxy

The behavior of misfit dislocations in InP/InGaAsP/InP double‐heterostructure wafers grown by liquid phase epitaxy has been investigated by x‐ray and photoluminescence (PL) topography. Misfit dislocations were found to be generated from the edges of all the wafers studied here. X‐ray topographs for angle‐polished wafers show that misfit dislocations exist within the upper InP layer and are located in close vicinity to the heterointerface. PL topography has been used to determine the misfit dislocation‐free area within the wafers. This area decreases monotonically with the increase of the upper InP layer thickness, and is almost independent of the quaternary layer thickness. The lattice misfit is necessary to be in the range 0∼−0.08% at room temperature for making the area without misfit dislocations as wide as possible. Generation of misfit dislocations is considered to be strongly related to the ’’melt back’’ of the InGaAsP edge growth.

Transmission electron microscope observation of dark‐spot defects in InGaAsP/InP double‐heterostructure light‐emitting diodes aged at high temperature

Dark‐spot defects revealed in the electroluminescence patterns of degraded InGaAsP/InP double‐heterostructure light‐emitting diodes that are operated at the current density of 8.0 kA/cm2 at 200 °C were investigated using transmission electron microscopy. Bar‐shaped defects lying in the direction of 〈100〉 or 〈110〉 were observed corresponding to the dark defects. These defects were precipitates of a certain kind of metal or compound and not ’’dislocationlike’’ ones.

Reduction of induced damage in GaAs processed by Ga+ focused‐ion‐beam‐assisted Cl2 etching

Damage in GaAs induced by Ga+ focused‐ion‐beam‐assisted Cl2 etching is studied by photoluminescence (PL) intensity measurements as functions of ion energy, ion dose, and substrate temperature. By decreasing the ion energy from 10 to 1 keV, the damage depth decrease to 1/5, where damage depth is taken as the thickness at which the PL intensity recovers by wet etching. The damage depth is shallower when the etching yield is larger with the same ion energy. By increasing the ion dose, the normalized PL intensity decreases, but damage depth is nearly constant. Over 1015 ion dose, the normalized PL intensity shows a constant value. By increasing the sample temperature, the damage depth becomes shallower. At 150  °C with ion energy of 1 keV, the damage depth is less than 0.5 μm, which is the detection limit of the PL measurement in GaAs substrate.