Xiangting Kong

Structure and photoluminescence of Mn-passivated nanocrystalline ZnO thin films

We have studied the structure and the photoluminescence of Mn-passivated nanocrystalline ZnO thin films. The ZnO thin films were prepared by thermally oxidizing ZnS:Mn films grown by low-pressure metalorganic chemical vapor deposition. The structural properties of the ZnO films were examined by X-ray diffraction and X-ray photoelectron spectroscopy. It was demonstrated that the Mn passivation could dramatically change the emission characteristics of nanocrystalline ZnO thin films. The photoluminescence spectra of the films with an optimized Mn-doped concentration showed only ultraviolet emission, while the green emission was fully quenched due to the Mn passivation of the ZnO nanocrystallite surface. A core-shell structure model of the surface passivation is presented. The note of the oxygen vacancy (Vo**) as the dominant recombination center for green emission is discussed.

Microstructure of GaN films grown on Si(111) substrates by metalorganic chemical vapor deposition

We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(I I I) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In0.1Ga0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed

Ridge InGaAs/InP multi-quantum-well selective growth in nanoscale trenches on Si (001) substrate

Metal organic chemical vapor deposition of InGaAs/InP multi-quantum-well in nanoscale V-grooved trenches on Si (001) substrate was studied using the aspect ratio trapping method. A high quality GaAs/InP buffer layer with two convex {111} B facets was selectively grown to promote the highly uniform, single-crystal ridge InP/InGaAs multi-quantum-well structure growth. Material quality was confirmed by transmission electron microscopy and room temperature micro-photoluminescence measurements. This approach shows great promise for the fabrication of photonics devices and nanolasers on Si substrate.

The Comparison of Current Ratio

This paper mainly describes the comparison of I_ON/I_OFF ratio and mobility between SiGe substrate and GaAs substrate In_0.23Ga_0.77As channel MOSFETs grown by metalorganic chemical vapor deposition. In order to make the comparison more reasonable, we choose the same size (Lg = 10 μm) for both the SiGe substrate and GaAs substrate MOSFETs. As for the SiGe substrate MOSFETs, its highest ON-current to the lowest OFF-current (I_ON/I_OFF) ratio is less than 1×103, while that of GaAs substrate MOSFETs are up to 4×10⁴ (both at a gate bias of 3 V). Due to the Ge diffusion into the InGaAs channel, it will make the intrinsic channel become an n-type doped semiconductor and then influence the pinchoff characteristics. The maximum effective mobility of SiGe substrate MOSFETs is 1800 cm²/V · s and that of GaAs substrate MOSFETs is up to 2090 cm2/V · s. The main reason for the higher mobility of GaAs substrate MOSFETs is maybe due to its smaller density interface trap density Dit and undoped InGaAs channel. Through comparing the performance, particularly the I_ON/I_OFF ratio and mobility between SiGe substrate and GaAs substrate MOSFETs, we aim to find out some feasible methods to improve the performance of InGaAs channel MOSFETs on SiGe substrate.

I_{\mathrm{\scriptscriptstyle ON}}/I_{\mathrm{\scriptscriptstyle OFF}}

We report high-mobility In0.23Ga0.77As channel MOSFETs grown on Ge/Si virtual substrate by metal-organic chemical vapor deposition for the first time. Through a low-temperature GaAs nucleation layer on Ge surface, a high-quality III-V MOSFET structure is obtained, with its etch pit density of 1.5 × 105 cm-2. The maximum effective mobility is up to 1880 cm2/Vs, extracted by the split C-V method. The highest ON-current to the lowest OFF-current (ION/IOFF) ratio of ~2000 has been obtained. The 8-μm channel-length devices exhibit a drain current of 60 mA/mm and a peak extrinsic transconductance of 20 mS/mm. These results indicate that the high-mobility III-V nMOSFETs on Si substrate can be realized and even used to act as nMOSFETs for the fabrication of future CMOS.

and Mobility Between SiGe Substrate and GaAs Substrate In 0.23 Ga 0.77 As Channel MOSFETs

We demonstrate high-performance In0.23 Ga0.77 As channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with high on-current to off-current (Ion/Ioff) ratio grown on semi-insulating GaAs wafers by metal-organic chemical vapor deposition (MOCVD). The 2 μm channel-length devices exhibit a peak extrinsic transconductance of 150 mS/mm and a drain current up to 500 mA/mm. The maximum effective mobility is 1680 cm2/Vs extracted by the split C-V method. Furthermore, the Ion/Ioff ratio is significantly improved from approximately 4.5 × 103 up to approximately 4.32 × 104 by controlling the etch thickness of In0.49 Ga0.51 P. The high drain current and high Ion/Ioff ratio of the In0.23 Ga0.77 As channel MOSFETs are achieved due to the high effective mobility and the low gate leakage current density.

High-Mobility In 0.23 Ga 0.77 As Channel MOSFETs Grown on Ge/Si Virtual Substrate by MOCVD

This letter reports the nanoscale spatial phase modulation of GaAs growth in V-grooved trenches fabricated on a Si (001) substrate by metal–organic vapor-phase epitaxy. Two hexagonal GaAs regions with high density of stacking faults parallel to Si {111} surfaces are observed. A strain-relieved and defect-free cubic phase GaAs was achieved above these highly defective regions. High-resolution transmission electron microscopy and fast Fourier transforms analysis were performed to characterize these regions of GaAs/Si interface. We also discussed the strain relaxation mechanism and phase structure modulation of GaAs selectively grown on this artificially manipulated surface.

High-Performance In0.23Ga0.77As Channel MOSFETs with High Current Ratio on/ off Grown on Semi-insulating GaAs Substrates by MOCVD

Epitaxial growth of III-V compound semiconductors on Si has attracted significant attention for many years due to the potential for monolithic integration of III-V based optoelectronic devices with Si integrated circuits. There are three major problems for GaAs monolithic epitaxy on Si, respectively the large lattice mismatch, the difference in thermal expansion coefficient, and growth of a polar material on a nonpolar substrate. Various dislocation reduction techniques have been proposed, such as graded SiGe buffer layers, thermal cycles annealing (TCA), and strained-layer superlattices (SLs) as dislocation filters. Unfortunately, these methods generally require relatively thick epitaxial layers and/or complex epitaxial process. This study relates to the heteroepitaxy of GaAs on nanopatterned Si substrates using the selective aspect ratio trapping method. The dislocations originally generated at the GaAs/Si interface are mostly isolated by the SiO2 side wall. High-quality GaAs nanowires have been grown on Si(001) substrates by metal-organic chemical vapor deposition. A method of two-step epitaxy of GaAs is performed to achieve a high-quality GaAs layer with a 217 arcsec narrow FWHM of HRXRD. Material quality was confirmed by Scanning electron microscope (SEM) and transmission electron microscopy (TEM). We also simulated the distribution of the light field on the nanoscale GaAs layer surround by Ag films used the FDTD method. The light field confined well in the 250nm width GaAs nanowire which can be used in the nanolasers on Silicon as light sources.