Benzhong Wang

Nanoscale epitaxial overgrowth process and properties of GaN layers on Si (111) substrates

Nanoscale epitaxial overgrowth has been explored to realize continuous specular GaN films on patterned SiO2∕GaN∕Si (111) substrates. We have employed both polystyrene-based nanosphere and interferometric lithographies to form the nanohole array patterns and then subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition. The nanoscale epitaxial overgrowth process of GaN layers is studied by scanning and transmission electron microscopy measurements. Optical spectroscopic methods such as microphotoluminescence and micro-Raman scattering show an improvement of the optical and crystalline quality in such overgrown GaN layers when compared to GaN simultaneously grown on bulk Si (111) without patterning. Realization of such thicker and good quality GaN layer would be useful to achieve III-nitride-based optoelectronic integration on Si substrates.

Nanopatterning and selective area epitaxy of GaN on Si substrate

Due to lack of suitable lattice matched substrates, III-Nitride materials are usually grown on sapphire, SiC, and silicon. The heteroepitaxy of GaN on these substrates often incorporates a high density of dislocation and point defects due to lattice and thermal mismatch. It is desirable to reduce the defect density in III-Nitrides in order to fabricate longer lifetime and high brightness light emitting diodes, lasers, and high-electron mobility transistors. In this context, nano-scale epitaxy on patterned Si substrates allows lateral growth, which eventually leads to a reduction of defect density and strain in the overgrown GaN films. Large area nano-patterning with dielectric masks would also be useful to fabricate highly-ordered and dense nitride nanostructures by selective area homo- and hetero-epitaxy.

MOCVD Behaviors of Two-Sized InGaAs Ordered Nano-Bar Arrays Grown Selectively on a GaAs Substrate

Nanosphere lithography was used to form a nano-scaled SiO 2 template on a GaAs substrate. Especially, a simple method for fabricating nanopatterns with multi feature sizes within one step has been invented. These nanopatterns, as a template, can be used to grow selectively ordered nanostructures arrays such as quantum dots, quantum bars with different feature sizes in one step. Two sized In 0.25 Ga 0.75 As nano-bar arrays have been successfully grown on a GaAs substrate by MOCVD.

Interfacial Properties, Surface Morphology and Thermal Stability of Epitaxial GaAs on Ge Substrates with High-k Dielectric for Advanced CMOS Applications

Epitaxial GaAs layers had been grown by metal organic chemical vapor deposition at 620°C on Ge(100) susbtrates. The surface roughness of the GaAs is greater than that of GaAs bulk wafers and epilayer morphology is influenced by miscut of the Ge substrate. The GaAs/Ge interface is of good quality and devoid of misfit dislocations and antisite defects. However, Ge diffusion into GaAs occurred during epitaxy and resulted in auto-doping. ZrO 2 was deposited by magnetron sputtering onto the epi-GaAs. Capacitance voltage measurements show that the TaN/ZrO 2 /epi-GaAs capacitor has an interfacical with more defects than a ZrO 2 /bulk GaAs interface. An improved interface with smaller frequency dispersion can be formed by atomic layer deposition of the high-k dielectric layer onto the epi-GaAs.

Self-organized growth of InP on GaAs substrate by MOCVD

Self-organized InP quantum dots having a staggered band lineup are formed in a GaAs matrix by MOCVD. Experimental results of photoluminescence show that the growth behaviors are different when the growth is carried out a different temperatures. Thicker and more smooth wetting layer are evident if the InP is grown at 600 degrees C. For the samples of InP grown at 490 degrees C, besides a weak PL peak resulting from the wetting layer, a strong PL peak located at 986 nm is observed. The luminescence can be attributed to radiative recombination of 0D electrons located in the InP dots and holes located in the surrounding regions. State filling of the 0D electrons is also observed for the type-II quantum dots.