Tatau Nishinaga

InP Layer Grown on (001) Silicon Substrate by Epitaxial Lateral Overgrowth

An InP epitaxial layer with a dislocation-free area was obtained for the first time on (001) Si substrate by using the epitaxial lateral overgrowth (ELO) technique. Most etch pits appeared in the region over the seed area on the ELO stripe. This indicates that the SiO2 film between the lateral overgrowth layer and the substrate prevented the propagation of the dislocations from the substrate to the lateral overgrowth layer. Spatially resolved photoluminescence showed that the optical quality of an InP ELO layer grown on Si was almost the same as that of a homoepitaxially grown InP layer and that the ELO technique is also useful to relieve stress caused by both the lattice mismatch and the difference in thermal expansion coefficient.

Effect of growth temperature on epitaxial lateral overgrowth of GaAs on Si substrate

The dependence of epitaxial lateral overgrowth (ELO) of GaAs on Si on the growth temperature of liquid phase epitaxy (LPE) has been studied. It is shown that the ratio of the ELO width to the thickness (ELO ratio) depends strongly on LPE growth temperature. When the growth temperature is chosen as high as 620°C, the ELO ratio equals 5.8. However, when the growth temperature is decreased to 500°C, the ELO ratio is increased to as large as 14. Molten KOH etching showed that only a few pits are present on the ELO layers. It is concluded that by employing low growth temperature, GaAs epitaxial layers with large ELO ratio and with only a few dislocations can be obtained.

Epitaxial lateral overgrowth of InP by liquid phase epitaxy

Abstract Epitaxial lateral overgrowth (ELO) of InP has been conducted for the first time by liquid phase epitaxy (LPE). The overgrowth has been studied for seeds in SiO 2 of 2.5 to 7 μm width using starlike and parallel patterns. A wide and flat ELO layer was grown on (001) and (111)B oriented substrates at growth temperature between 773 and 873 K. No etch pits were found in the overgrowth regions. For (001) oriented substrates, the seed aligned away from 〈100〉 and 〈110〉 and their equivalent directions brought the maximum overgrowth up to 100 μm whereas the seed aligned adjoining these directions brought almost no overgrowth. On the other hand, for (111)B oriented substrates, the seed aligned away from 〈110〉 and its equivalent directions brought the maximum overgrowth up to 140 μm whereas the seed aligned adjoining these directions brought almost no overgrowth. The maximum ratio of width to thickness of 47 for (111)B ELO layer was obtained. This value is much larger than that of the (001) ELO layer of 17.

Surface diffusion length of cation incorporation studied by microprobe-RHEED/SEM MBE

Abstract The surface diffusion of group III atom incorporation in the MBE of GaAs and InAs is reviewed. First the diffusion length of incorporation on the (001) top surface with the (111)A or (411)A side surfaces of V grooves is discussed. It is shown that the diffusion length takes the same value for both cases and is inversely proportional to the arsenic pressure. The same relationship is also obtained for the diffusion of In in InAs MBE. However, the diffusion length of Ga on (111)B shows an inverse parabolic dependence of the arsenic pressure. It is suggested that on the (001) surface two As 4 molecules meet to give active As atoms for the growth. On the other hand, the behavior of the As 4 molecule on the (111)B surface is still not clear. The ratio of the surface diffusion coefficient on (111)B and that on (001) is calculated. It is found that the ratio takes a value of around 140. With this ratio, the incorporation life times τ inc on (111)B and (001) surfaces are calculated as functions of arsenic pressure. It is found that the lines of the incorporation life time intersect at the arsenic pressure where flow inversion occurs.

Optimization of growth condition for wide dislocation-free GaAs on Si substrate by microchannel epitaxy

The growth condition dependence of the microchannel epitaxy (MCE) width-to-thickness ratio (W/T ratio) was studied systematically. The result shows that by optimizing the line seed separation and growth temperature, the GaAs layer with a high W/T ratio has been grown on GaAs-coated Si substrate, respectively, at 500 μm and 530°C. In this work, GaAs MCE layers with a high W/T ratio of 17.5 were obtained. Furthermore, by employing the optimized growth condition, GaAs layers with a wide dislocation-free region on a Si substrate were obtained after the growth of 7 h. Molten KOH etching showed that the width of the dislocation-free region is about 43 μm for the sample grown for 3 h. The width is enough to fabricate devices such as vertical cavity surface emitting lasers (VCSELs).

Microchannel epitaxy: an overview

Abstract A new concept of epitaxy named microchannel epitaxy (MCE) is presented. In MCE, lattice information is transferred through narrow microchannels while the transfer of defect information is prevented by the presence of amorphous film at the epitaxial layer–substrate interface. Two types of MCE, vertical and horizontal MCEs, are demonstrated. In the present article, a special focus is given on the horizontal MCE, which we call simply MCE. MCE is composed of selective area epitaxy in the narrow microchannel and successive epitaxial lateral growth. It was demonstrated that flat MCE layers have been successfully obtained for GaAs and InP on Si substrates. Although dislocations propagate through the microchannel into the grown layer, wide dislocation-free regions have been obtained outside this dislocated area. MCE with high width-to-thickness ratio is successfully achieved by molecular beam epitaxy by sending molecular beams with a low angle to the substrate surface.

Spatially resolved photoluminescence of laterally overgrown InP on InP-coated Si substrates

Optical properties of InP grown by ELO (epitaxial lateral overgrowth) on InP-coated Si substrates were characterized by spatially resolved photoluminescence. Intensity of the photoluminescence spectra of these layers was found to be as strong as that of InP homoepitaxially grown on InP substrates. The luminescence spectra showed a small FWHM of 23 meV and no shift in wavelength was seen across the ELO layers. This means almost no stress exists in InP ELO layers on Si substrates. It is concluded that stress free InP has been obtained successfully on Si substrates. Simulation to evaluate stress in ELO layers was conducted and a good agreement with the experiments was obtained.

Interface supersaturation in microchannel epitaxy of InP

By employing microchannel epitaxy (MCE), it became possible to reduce the dislocation density in liquid phase epitaxy (LPE) of InP so that steps supplied from only one screw dislocation can cover the whole surface of MCE island. This enabled us to measure interstep distance by AFM and to calculate interface supersaturation even in metallic solution with the help of Cabrera and Levine formula by assuming appropriate value of interface free energy. The interface supersaturation was found being ranged from 0.02 to 0.05 upon various experimental conditions. A minimum interface supersaturation was realized when the growth temperature and cooling rate were chosen as 500°C and 0.05°C/min, respectively. The ratio of width to thickness of the grown MCE layer, which is defined as W/T ratio, was found to increase rapidly with the decrease of the interface supersaturation. A W/T ratio as high as 20 was accomplished under the growth condition where minimum interface supersaturation can be realized.

Coalescence in microchannel epitaxy of InP

Abstract We have studied the lateral coalescence in microchannel epitaxy (MCE) of InP by LPE. In the present study, we suggest that there are two modes of the coalescence, “one-zipper” and “two-zipper”. New patterns of microchannels were designed to realize these two coalescence modes. The coalesced MCE islands were chemically etched and it was found that dislocations were usually generated in the coalesced region when the growth was carried out in the “two-zipper” mode; however, when the growth occurred in the “one-zipper” mode, dislocations were not found in the coalesced region. It is concluded that by conducting the growth in the “one-zipper” mode, the formation of dislocations in the coalesced region can be avoided.

Periodic supply epitaxy: a new approach for the selective area growth of GaAs by molecular beam epitaxy

Abstract Selective growth of GaAs on a GaAs substrate with a SiO 2 patterned mask has been carried out by molecular beam epitaxy at 630°C, using molecular beams of Ga and As 4 as sources and employing a periodic supply epitaxy technique for the first time. The GaAs crystalline nuclei deposited on the mask surface are decomposed and the atoms adsorbed on the mask surface are evaporated or allowed to migrate until they are captured by the single crystalline epitaxial layer. A wide depleted zone is then formed and the polycrystals of GaAs are located beyond this area. The surface migration is shown to influence drastically the thickness of the grown layer. The epitaxial layer obtained is flat and smooth even for the (001) substrates, since the lateral flux prevents the decomposition of GaAs on the free surface of the epitaxial layer. The growth technique is discussed in details, together with an analysis of the important parameters for the selective growth by periodic supply epitaxy.