Xian Ye

Growth of stacking-faults-free zinc blende GaAs nanowires on Si substrate by using AlGaAs/GaAs buffer layers.

Vertical GaAs nanowires on Si (111) substrate were grown by metal organic chemical vapor deposition via Au-catalyst vapor-liquid-solid mechanism. Stacking-faults-free zinc blende nanowires were realized by using AlGaAs/GaAs buffer layers and growing under the optimized conditions, that the alloy droplet act as a catalyst rather than an adatom collector and its size and composition would keep stable during growth. The stable droplet contributes to the growth of stacking-faults-free nanowires. Moreover, by using the buffer layers, epitaxial growth of well-aligned NWs was not limited by the misfit strain induced critical diameter, and the unintentional doping of the GaAs nanowires with Si was reduced.

Experimental and theoretical investigations on the phase purity of GaAs zincblende nanowires

Interesting phenomena of GaAs nanowire growth have been observed. The nanowires were grown by metal-organic chemical vapor deposition (MOCVD) on GaAs (1?1?1)B substrates with an Au catalyst at 464 ?C. The growth rates of all nanowires were almost the same for a fixed density of Au nanodrops. TEM analysis demonstrates a stacking-fault-free zincblende structure of the nanowires even when their radius is reduced to as small as 12 nm. A theoretical model is developed that is capable of describing the critical radius of zincblende to wurtzite phase transition as a function of vapor supersaturation and material constants. The model shows that the surprising prevalence of the zincblende structure should originate from very high supersaturations during MOCVD.

Control of the crystal structure of InAs nanowires by tuning contributions of adatom diffusion

The dependence of crystal structure on contributions of adatom diffusion (ADD) and precursor direct impingement (DIM) was investigated for vapor-liquid-solid growth of InAs nanowires (NWs). The ADD contributions from the sidewalls and substrate surface can be changed by using GaAs NWs of different length as the basis for growing InAs NWs. We found that pure zinc-blende structure is favored when DIM contributions dominate. Moreover, without changing the NW diameter or growth parameters (such as temperature or V/III ratio), a transition from zinc-blende to wurtzite structure can be realized by increasing the ADD contributions. A nucleation model is proposed in which ADD and DIM contributions play different roles in determining the location and phase of the nucleus.

Design Net-Grid Subwavelength Gratings for High Quantum Efficiency Photodetectors

Subwavelength gratings (SWGs) that consist of net-grid structure are designed as infrared reflectors in this paper. By rigorous coupled wave approach (RCWA) and finite difference time domain (FDTD) method, we simulate its reflectivity which can reach 99.98% at 1.55μm while maintaining reflectivity higher than 99% across the 1.47-1.59μm wavelength range. We introduce SWG reflectors as the bottom mirrors in resonant cavity enhanced photodetectors (RCE PDs). RCE PDs quantum efficiency is increased to 95.7% at 1.55μm and the device has a significant size reduction compared with only using DBR bottom mirror.

Analysis of strain energy in nanowire heterostructures with component gradient buffer section

In this paper, analytical method is employed to analyze the system strain energy and critical diameter of one kind of longitudinally heterostructure nanowire which contains component gradient buffer sections. Based on the critical diameter model of F. Glas in heterostructure nonawires, calculation has been made to research on how does single-layer thickness and total thickness of gradient buffer effect the critical radius of the system. The results illustrate that component gradient buffer layer can effectively reduce the system strain energy, and the thinner the single-layer buffer section thickness , the more obvious the improvement of its critical radius; if the lattice mismatch of the heterostructure nonawires is smaller, the strain energy can be reduced more significantly, also the greater rate of increase of its critical radius. The freedom cut of the nonawires diameter can be realized by controlling the component and thickness of buffer sections. Using Au assistant MOVCD method, we can get high-quality nonawires with component gradient buffer sections, in contrast to the bad quality SEM image of the nonawires without buffer layers, which effectively prove the above conclusions.

Study on resonant cavity enhanced photodetector using subwavelength grating

Sub-wavelength gratings are used in the new photodetector in this paper. The detectivity is enhanced by excitation of surface plasma waves (SPW) using a Metal Aperture Arrays grating. Sub-wavelength dielectric grating is used to replace the top Bottom Distributed Bragg Reflectors(DBR).

InP nanowires with various morphologies formed by au-assisted metal-organic chemical vapor deposition

InP nanowires were grown on InP(100) substrates via VLS mechanism with Au particles as catalyst. Various morphologies of the nanowires such as straight, L-branch, Y-branch, K-branch, bottle-shape, cone-shape, needle-shape were obtained.

Growth of GaAs nanowires with various thickness of Au film

GaAs nanowires were grown by the metal organic chemical vapor deposition on the GaAs(111)B substrates via Vapor-Liquid-Solid mechanism with various Au film thickness. Experiment results indicated that thicker Au film results in larger diameters, more dispersed size distribution, and lower density of the nanowires. All NWs are straight from base to top, and no lateral growth occurs. The growth rate of nanowires slightly increases with Au film thickness. It indicates that the growth of GaAs NWs is mainly promoted by the catalyzed chemical reaction at the drop surface, the Au particles surface density could influence the growth rate, and contribution of diffusion from the adatom could be neglected.

Study on high speed photodetectors with plasmonics flilter

A new photodetector was designed with Metal Aperture Arrays filter in this paper. The shape and dimensions of the holes in an arrays do influence its transmission spectrum compare to the conventional photodetector. Hole array and annular aperture arrays were discussed.

Design and fabrication of multichannel tunable photodetector array

A long wavelength multichannel tunable photodetector array was fabricated based on multistep Fabry-Pérot filter by using the heteroepitaxy growth of InP-In0.53Ga0.47As-InP PIN structure on a GaAs based GaAs/AlAs Fabry-Pérot filter structure. High quality heteroepitaxy was realized by employing a thin low temperature buffer layer. The array can detect multiple channels, and the tuning range of each detector is about 10nm. A spectral linewidth of 0.5nm, a quantum efficiency over 25%, and a 3dB bandwidth of 9.2GHz were simultaneously obtained.