Jingwei Guo

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.

Growth of InAs quantum dots on GaAs nanowires by metal organic chemical vapor deposition.

InAs quantum dots (QDs) are grown epitaxially on Au-catalyst-grown GaAs nanowires (NWs) by metal organic chemical vapor deposition (MOCVD). These QDs are about 10-30 nm in diameter and several nanometers high, formed on the {112} side facets of the GaAs NWs. The QDs are very dense at the base of the NW and gradually sparser toward the top until disappearing at a distance of about 2 μm from the base. It can be concluded that these QDs are formed by adatom diffusion from the substrate as well as the sidewalls of the NWs. The critical diameter of the GaAs NW that is enough to form InAs QDs is between 120 and 160 nm according to incomplete statistics. We also find that these QDs exhibit zinc blende (ZB) structure that is consistent with that of the GaAs NW and their edges are faceted along particular surfaces. This hybrid structure may pave the way for the development of future nanowire-based optoelectronic devices.

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.

Growth and optical properties of InP nanowires formed by Au-assisted metalorganic chemical vapor deposition: Effect of growth temperature

Vertical indium phosphide nanowires (NWs) were grown at different temperatures by metalorganic chemical vapor deposition via a gold (Au)-assisted vapor-liquid-solid mechanism. At a low growth temperature (420 °C), the lengths of the NWs were diameter independent, which indicated that the NWs were grown with significant contributions from the direct impingement of the precursors onto the alloy droplets. In this process, the droplet acts as a catalyst rather than an adatom collector. However, at a high growth temperature (480 °C), the lengths of the NWs were inversely diameter dependent. The wurtzite percentage of NWs increases with the growth temperature. Room temperature photoluminescence properties of NWs grown under different temperatures were investigated.

Realizing Zinc Blende GaAs/AlGaAs Axial and Radial Heterostructure Nanowires by Tuning the Growth Temperature

Vertical zinc blende GaAs/AIGaAs heterostructure nanowires were grown at different temperatures by met-alorganic chemical vapor deposition via Au-assisted vapor-liquid-solid mechanism. It was found that radial growth can be enhanced by increasing the growth temperature. The growth of radial heterostructure can be realized at temperature higher than 500°C, while the growth temperature of axial heterostructure is lower than 440°C. The room temperature photoluminescence properties of the nanowires were investigated and the relevant growth mechanism was discussed.

Influence of GaAs substrate on the transmission performance of epitaxially grown Fabry-Peerot f ilter

The influence of GaAs substrate on the transmission performance of a multi-film Fabry-Peerot filter (FPF), fabricated by metalorganic chemical vapor deposition epitaxial growth on GaAs substrate, is investigated using the transfer matrix method. On the basis of the theoretical simulation, we determine that the quality of the resonant transmission peak of this epitaxially grown FPF (EG-FPF) deteriorates through splitting when the substrate is taken into account. Rapid periodic oscillation of peak-transmittivity along with the alteration of substrate thickness is also observed in the simulation results. Finally, a remarkably improved transmission performance of the EG-FPF is obtained by thinning the substrate down to a suitable thickness range through well-controlled grinding and polishing.

Si-based tunable flattop photodetector with a stepped Fabry–Perot cavity

This paper presents the design and analysis of a Si-based tunable flattop photodetector realized by the introduction of a stepped Fabry-Perot cavity, which can be thermally tuned via applying tuning power on its tuning electrode. By using a transfer matrix method, the spectral response of the photodetector is simulated in detail, indicating a flattop line shape can be achieved with an optimum step height. A trade-off residing in this device between the free spectrum range and the ease of fabrication of step height is also revealed and analyzed. In the final design of the photodetector, 1 dB linewidth of 0.5 nm, 3 dB linewidth of 0.8 nm, 6 dB linewidth of 1.2 nm, peak quantum efficiency of 40%, tuning efficiency of 91 mW/nm are theoretically obtained. We discuss the epitaxial growth and fabrication of the photodetector in the end, exhibiting the mature technique available for this device.

Growth of n-doped GaAs nanowires by Au-assisted metalorganic chemical vapor deposition: effect of flux rates of n-type dopants

N-doped GaAs nanowires (NWs) were grown on GaAs (111) B substrate by means of vapor-liquid-solid (VLS) mechanism in a metalorganic chemical vapor deposition (MOCVD) system. Two flux rates of n-type dopants used for GaAs NWs growth were researched. For comparison, undoped GaAs NWs were grown at the same conditions. It is found that all NWs are vertical to the substrate and no lateral growth occurs. The growth rate is proportional the flux rates of n dopant. It is observed that there is Gibbs-Thomson effect in doped NWs. Pure zinc blende structures without any stacking faults from bottom to top for all three samples were achieved.

Realization of vertical GaAs/InAs nanowire heterostructures on Si substrate

GaAs/InAs nanowire heterostructures are grown on Si(111) substrate by metal organic chemical vapor deposition via Au-catalyst vapor-liquid-solid mechanism. Nanowires vertical to the substrate are realized by using GaAs/AlGaAs buffer layers. Straight InAs wire is grown axially on the GaAs nanowire by inserting a composition-graded InxGa1-xAs buffer segment between the two lattice mismatched materials. This work helps open new possibilities for the integration of III-V nanowire heterostructures on Si.