Kangsa Pak

Reduction of threading dislocation density in InP‐on‐Si heteroepitaxy with strained short‐period superlattices

We applied multistrained short‐period superlattices (SSPSs) and GaP buffer layers to the InP‐on‐Si heteroepitaxy, in order to suppress the generation of threading dislocations. As a result, it was found that the density of threading dislocations in an InP/SSPSs/GaAs/SSPSs/GaP/Si structure including (InAs)m(GaAs)n SSPSs and (GaAs)i(GaP)j SSPSs was remarkably reduced, compared with that in the InP/GaP/Si structure. Misfit dislocations lying along the 〈011〉 directions were observed at heterointerfaces in the InP/SSPSs/GaAs/SSPSs/GaP/Si structure. Therefore, the lattice mismatch strain was stepwise accommodated by the generation of misfit dislocations at the heterointerfaces. From these results, it was clarified that multi‐SSPSs are effective for reducing the density of threading dislocations in heteroepitaxy with a large lattice mismatch.

Ge segregation and its suppression in GaAs epilayers grown on Ge(111) substrate

The interdiffusion of the compositional atoms was investigated at heterointerface between a GaAs epilayer and a Ge(111) substrate by secondary ion mass spectroscopy. When a thin AlAs layer is applied initially, diffusion of Ge into the GaAs epilayer was suppressed effectively. An abrupt heterointerface was successfully realized in relatively high temperature growth. The interdiffusion process at the AlAs‐Ge heterointerface was clarified in high temperature growth, which was dominated by the temperature‐assisted segregation of Ge atoms during the AlAs growth rather than thermal diffusion. The compositional diffusion of Al atoms into the GaAs epilayer was also observed, which was enhanced by the Ge segregation in the structure of GaAs/AlAs/Ge substrate grown at higher temperature.

In-situ maskless selective area epitaxy of GaAs using a low-energy Ga focused ion beam

Abstract In-situ maskless selective area epitaxy of GaAs was performed for the first time with a low-energy Ga focused ion beam (FIB) and an As 4 molecular beam. A newly developed low-energy FIB system was employed in the experiments, which can be utilized in the retarding mode with a substrate bias of zero. The low energy Ga FIB and the As 4 molecular beam were supplied simultaneously on the GaAs(100) substrate. The incident energy ( E i ) of Ga FIB and the substrate temperature ( T s ) Were varied from 30 to 500 eV and from 270 to 500°C, respectively. The maskless selective deposition of GaAs with a diameter of ∽ 180 μm can be achieved below E i of 200 eV. The results of μm-RHEED measurement showed that the GaAs film was a single crystal above T s of 400°C. All the selectively grown GaAs had flat surfaces.

Segregation and interdiffusion of In atoms in GaAs/InAs/GaAs heterostructures

The segregation and interdiffusion of In atoms in the GaAs/InAs/GaAs heterostructures were investigated by secondary‐ion mass spectroscopy. When the 1‐ML‐thick InAs layer was grown in a layer‐by‐layer growth mode with no dislocations, the segregation of In atoms became marked with the increase of the growth temperature. However, the segregation was observed even at a relatively low growth temperature of 400 °C in molecular beam epitaxy. It was found that the segregation was markedly enhanced by dislocations near the heterointerface when thick InAs layers were grown in a three‐dimensional island growth mode. The interdiffusion of In atoms toward the growth direction occurred after thermal annealing, which could be assisted by vacancies propagating from the film surface into the epilayer. It became apparent that the interdiffusion was effectively suppressed by a thin AlAs layer inserted in the GaAs cap layer.

Behavior of macrosteps and grooves during LPE growth as observed by photoluminescence images

Abstract Observations were made of photoluminescence (PL) images from cleaved surfaces of GaP LPE layers doped with Zn and O. The dark region was found to terminate at a macrostep riser, which showed behavior of the macrostep during the LPE growth. It was found that the horizontal velocity of the macrostep decreased as the macrostep height increased. A groove was created from a macrostep when the forward-going emission of atomic steps was prevented at the bottom corner of the macrostep. The dark region associated with the macrostep riser is explained as arising from a low rate of Zn-O incorporation at a slow moving front of the atomic step.

Suppression of threading dislocation generation in GaAs-on-Si with strained short-period superlattices

Abstract We investigated the suppression of threading dislocation generation in GaAs-on-Si(100) with strained short-period superlattices by reflection high-energy electron diffraction and transmission electron microscopy. A two-dimensional growth mode was kept during the lattice relaxation process. As a result, the density of threading dislocations in the GaAs epilayer was markedly reduced. A lattice mismatch of 4% was accommodated at hetero-interfaces by generating misfit dislocations in the directions of 〈011〉.

Realization of mirror surface in (111)- and (110)-oriented GaAs by migration-enhanced epitaxy

The layer-by-layer growth mode was readily realized on exactly oriented GaAs(111)B and GaAs(110) substrates by migration-enhanced epitaxy. This growth mode results in a mirror surface with low hillock density of ∼103 cm−2 which is 3 orders of magnitude lower than the density obtained by conventional MBE growth.

Initial Growth Mechanism of GaAs on Si(110)

We report the initial growth mechanism of GaAs on Si(110) by molecular beam epitaxy. From in-situ reflection high-energy electron diffraction (RHEED) measurements we infer an initial two-dimensional growth mode. Streak RHEED patterns were observed up to about 20 Athickness of GaAs epitaxial growth. With further deposition, extra spots appeared due to twins. We propose a model in which the twins are formed from antiphase domain boundaries.

Two-Dimensional Computer Analysis of Liquid Phase Epitaxy

Two-dimensional computer analysis of LPE is performed to find the mechanism of edge growth. The edge height and nonuniformity factor are calculated as a function of time for various growth parameters. The calculations are compared with experiment and good agreement is found between them. Three methods are recommended for minimizing edge growth. The first is to employ higher super-saturation and short growth time. The second is to set the area of the substrate as close as possible to that of the solution bottom. To realize the latter, it is necessary to use a substrate wider than the solution bottom, and we suggest putting a weight on the solution to obviate the nonwetting region on the substrate in the corner of the slide boat well. The third is to choose a special shape of the solution well. It is concluded that edge growth is due to diffusion from the solution on the nongrowth region adjacent to the growth edge.

The Origin of Dark Region in LPE GaP Associating with Macrostep Riser

The origin of the dark region in LPE grown GaP crystals associated with macrostep is investigated by observation of photoluminescence (PL) image and spatially resolved photolumenescence (SRPL) spectroscopy. PL image from the cleaved surface of undoped, N, S, and Zn doped layers showed that the dark region appeared only when nitrogen was doped irrespective of simultaneous doping of S or Zn. The result of SRPL measurement showed that the concentration of N was lower in the dark region compared with the bright region. This could be explained by the difference of the step velocity on the riser and the tread of the macrostep.