Xiaoye Wang

Effects of rapid thermal annealing on self-assembled InGaAs/GaAs quantum dots superlattice

Postgrowth rapid thermal annealing was used to study the relaxation mechanism and optical properties of InGaAs/GaAs self-assembled quantum dots superlattice grown by molecular beam epitaxy. It is found that a significant narrowing of the luminescence linewidth (from 80 to 42 meV) occurs together with about 86 meV blue shift at annealing temperature up to 950°C. Double crystal X-ray diffraction measurements show that the intensity of the satellite diffraction peak, which corresponds to the quantum dots superlattice, decreased with the increasing annealing temperature and disappeared at 750°C, but recovered and increased again at higher annealing temperatures. This behavior can be explained by two competing relaxation mechanisms; interdiffusion and favored migration. The study indicates that a suitable annealing treatment can improve the structural properties of the quantum dots superlattice.

Switching from Negative to Positive Photoconductivity toward Intrinsic Photoelectric Response in InAs Nanowire

Negative photoconductivity (NPC) and positive photoconductivity (PPC) are observed in the same individual InAs nanowires grown by metal-organic chemical vapor deposition. NPC displays under weak light illumination due to photoexcitation scattering centers charged with hot carrier in the native oxide layer. PPC is observed under high light intensity. Through removing the native oxide layer and passivating the nanowire with HfO2, we eliminate the NPC effect and realize intrinsic photoelectric response in InAs nanowire.

Enhanced near-infrared photoluminescence from isoelectronic luminescent centers in sulfur-implanted silicon with copper or silver coimplantation

Enhanced near-infrared photoluminescence (PL) from sulfur-related isoelectronic luminescent centers in silicon was observed from thermally quenched sulfur-implanted silicon in which additional copper or silver ions had been coimplanted. The PL from the sulfur and copper coimplanted silicon peaked between 70 and 100K and persisted to 260K. This result strongly supports the original conjecture from the optical detection of magnetic resonance studies that the strong PL from sulfur-doped silicon comes from S–Cu isoelectronic complexes [Frens et al., Phys. Rev. B 46, 12316 (1992); Mason et al., ibid. 58, 7007 (1998).].

Nanoscale opening fabrication on Si (111) surface from SiO2 barrier for vertical growth of III-V nanowire arrays

We reported here a selectively additive process to fabricate nanoscale openings of an Si (111) surface from an SiO2 barrier layer. Such nanoscale openings are made for the growth of vertical III-V nanowires. The Si (111) surface protected by a patterned SiNx layer was thermally oxidized, which resulted in a selectively added SiO2 barrier layer. After removing the SiNx, nanoscale openings of the Si (111) surface were exposed for the nanowire growth. Arrays with patterned nanoholes of varied diameters from 60 nm to 334 nm have been used for position-controlled catalyst-free growth of vertical InAs nanowire arrays by metal-organic chemical vapor deposition. Correlations between the nanohole diameter and the diameter, length and growth yield of as-fabricated nanowire arrays have been investigated, showing a repeatable stability. This technique offers an alternative approach for the fabrication of novel III-V nanowire devices using vertical array configuration. A lateral thermal oxidation effect led to a smaller size of the Si opening than that of the SiNx protection nanoislands; therefore, the technique also offers a controllable way to produce nanoholes with an ultra-small diameter.