Synthesis of Au-assisted GaAs Nanowires on Si Substrate by Pulsed-jet Epitaxy Method

GaAs nanowires (NWs) assisted Au catalyst on the Si (111) substrate have been synthesized by employing the pulsed-jet epitaxy method. The effect of growth conditions was evaluated by changing the formation and the growth direction of the NWs. Increasing the Au droplet diameter, the number density of NWs reduced and the length of NWs became longer. In the higher growth temperature, the distribution of the growth direction on the nanowire axis was small, and the NWs grow to perpendicular direction to a substrate. However, the desorption of As restrain the growth of NWs more than 550 ℃.departmental bulletin pape

Site Selective Growth of GaAs-NWs on Patterned Si Substrate

Catalyst-free GaAs-nanowire (GaAs-NWs) have been studied . But, It doesn't achieve to growth GaAs-NWs on Si(001) substrate looking toward the opto-electronic integrated circuit (OEIC) and Micro Electro Mechanical systems (MEMS). So we attempted to make site selective growth of GaAs-NWs by using patterned Si substrate and investigated the flux condition of maximum GaAs-NWs density. We found that it is possible to selective growth of GaAs-NWs by patterned Si substrate and GaAs-NWs or GaAs layer morphology depend on Ga flux. For detail, Ga flux and As flux are less than 0.25 [ML/s] and 1.0 [ML/s] for maximum GaAs-NWs density. Additionally, we concluded relation between Ga flux and Ga droplet have an effect on relation between Ga flux and GaAs-NWs density.departmental bulletin pape

Effects of Si Dopant Gas Flow Sequence on Electrical Properties of GaAsN Films Grown by ALE

The effects of Si dopant gas flow sequence on electrical properties of GaAsN films have been investigated. The Si-doped and non-doped GaAsN films were grown on semi-insulating GaAs(001) substrate at substrate temperatures of 480, 500 and 520 oC by atomic layer epitaxy (ALE). The non-doped GaAsN films grown by ALE were p-type due to residual carbon atoms worked as acceptor. The Si doped films were also p-type, however carrier density and mobility were smaller than those of the non-doped films. The difference on carrier density between non-doped and Si-doped films was consistent with Si concenteration in the films. Decrease of carrier mobility could be explained by increasing ionized scattering caused by Si. These suggested that Si atoms worked as donor.departmental bulletin pape

Misfit Dislocations of Initial Growth Stage in InGaAs/GaAs(001)Interface Observed Using X-ray Diffraction and Topography

Reciprocal space mapping (RSM) and X-ray topography (XRT) were performed to understand the anisotropies of misfit dislocations (MDs) formed in the initial growth stage of InGaAs on GaAs(001). The MDs densities increased with increasing both In composition and the film thickness, and it highly depended on the film thickness rather than the In composition. Anisotropies in MDs distribution observed by XRT were good agreement with those observed by RSM. In addition, the 15% of Burgers vectors for all MDs could be identified by XRT.departmental bulletin pape

Evaluation Method of Thin Films in Consideration of Penetration Depth of Excitation Light by Raman Spectroscopy

Raman measurements was performed using two different wavelengths lasers for three different kinds of thickness GaAsN / GaAs thin film. We have compared two methods of fitting. One was fitted with TO and LO peak of sample and another was fitted with 3 peaks, TO, LO and the substrate GaAs LO peak. It was found that the signal from the substrate was superimposed on the signal from the upper layer. In the care of thin film Raman measurement, it is necessary either using the excitation light having the shorter penetration depth than the film thickness or analyzing process to eliminate the influence of the substrate.departmental bulletin pape

Electrical properties of GaAsN/GaAs-superlattice films with different N distributions fabricated by atomic layer epitaxy

The effects of nitrogen (N) distribution on the electrical properties of GaAsN films were evaluated by intentionally changing the N distribution using atomic layer epitaxy (ALE) and post-annealing. The N distribution was controlled in the growth direction by growing superlattice (SL) thin films repeatedly growing 1 GaAsN layer and 0, 3, and 5 layers of GaAs by ALE. These films were referred to as (1:0), (1:3), and (1:5), respectively. To change the N distribution in the same thin film, N atoms were diffused by post-annealing. Changes in N distribution were evaluated by X-ray diffraction as changes in GaAsN superstructure. N atoms diffused from GaAsN layers to the adjacent layers in (1:3) films annealed above 750 °C, while they remained stable in those of (1:5) films annealed at temperatures up to 850 °C. The carrier mobility of both films increased monotonically with the annealing temperature. The concentration of ionized scattering centers decreased significantly in films annealed at 650 °C (independent of their N distributions) owing to the elimination of donor-type defects by annealing. Contrarily, the concentrations of N-induced scattering centers in (1:5) films annealed below 900 °C were similar, while those in (1:3) films annealed above 750 °C decreased significantly, in agreement with the N-atom diffusion behavior of GaAsN layers. Thus, N-distribution homogenization can be related to the reduction of N-induced scattering centers

Effects of Annealing in GaAsN Films with Different N Distributions Measured by Raman Spectroscopy

GaAsN thin films with nonhomogenious N distribution which average nitrogen concentration was 0.5% was grown the atomic layer epitaxy method. The sample was evaluated by Raman spectroscopy. No difference between normal mixed crystal film and most nonhomogenious N distribution film was obtained. It was impossible to directly detect thedetect the N nonhomogeneity in dilute N concentration. As a result of annealing these samples, the crystallinity became the best at 700 ℃ and disordered thereafter. This was not consistent with the result of the mobility changedepartmental bulletin pape