tung luong - Academia.edu (original) (raw)

Papers by tung luong

Physical Chemistry Chemical Physics, 2021

In this paper, we systematically examine the effects of charged impurity doping and electric fiel... more In this paper, we systematically examine the effects of charged impurity doping and electric field on the HC of monolayer β12-borophene.

2017 China Semiconductor Technology International Conference (CSTIC), 2017

The effect of different buffer layers on the RF losses of GaN-based high-mobility-transistors (HE... more The effect of different buffer layers on the RF losses of GaN-based high-mobility-transistors (HEMTs) on Si substrate has been studied. It is found that the electron inversion layer induced by the residual tensile stress in AlN buffer is responsible for a dominant loss factor. It is first time such mechanisms of the RF loss of GaN/Si is discussed. It is proven that using a thin high-low-high temperature (HLH) AlN buffer reducing the tensile stress in AlN consequently reduces the RF loss.

2016 China Semiconductor Technology International Conference (CSTIC), 2016

Two inches size with high quality layered growth of MoS2 was achieved by P... more Two inches size with high quality layered growth of MoS2 was achieved by PLD on c-plane sapphire substrate. 2~3 monolayer MoS2 was obtained within 2 inches wafer estimated from Raman analysis and confirmed by cross-sectional view of TEM. Additionally, the oxide states of Mo 3d core level spectra of MoS2, analyzed by XPS, can be effectively reduced by adopting a post sulfurization process in H2S. The post process also improve the photoluminescence (PL) of MoS2 as well as the electrical characteristic of MoS2 FET due to elimination the Mo oxide in the grown film.

Electronic Materials Letters, 2015

An advanced AlGaN/GaN HEMT structure, grown on a sapphire substrate by MOCVD utilizing a high tem... more An advanced AlGaN/GaN HEMT structure, grown on a sapphire substrate by MOCVD utilizing a high temperature (HT) AlN interlayer (IL) and a multilayer high-low-high temperature (HLH) AlN buffer layer, demonstrates a superior performance both in breakdown voltage (>200 V) and maximum drain current (IDSS = 667 mA/mm). The HT AlN IL produces an additional compressive strain into the above GaN layer. Accordingly, an AlGaN barrier, grown on the more compressive GaN, introduces less tensile strain leading to an improvement in surface morphology (RMS = 0.19 nm in 2 × 2 µm 2), a remarkable increase in 2DEG mobility by 46% (µs = 1900 cm 2 /Vs) and a decrease in densities of defects acting as paths for the leakage current through the AlGaN barrier. A high semi-insulating buffer is achieved by eliminating leakage paths both through the buffer layer and the buffer-substrate interfacial layer. These result from an increase in unintentional carbon introduced by AlN layers, especially by a low temperature AlN layer; which are grown under low pressure (50 Torr). Lastly, the decrease in AlGaN barrier tensile strain and low leakage current in the advanced HEMTs structure using an HT AlN IL and an HLH AlN buffer are promising for an improvement in AlGaN/GaN HEMTs' reliability.

physica status solidi (RRL) - Rapid Research Letters, 2015

Chemical Vapor Deposition, 2014

The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (H... more The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) grown using metalorganic (MO)CVD by engineering structure, barrier strain, and unintentional carbon incorporation, are demonstrated in this work. Both normal HEMT structure (with a high temperature (HT) AlN buffer) and advanced HEMT structure (with a highlow-high temperature (HLHT) AlN buffer, and a HT AlN interlayer (IL)) present a breakdown voltage higher than 200 V, while a much smaller breakdown voltage of 17 V is measured on the conventional structure using a low-temperature GaN buffer. The HT AlN IL inserted in the middle of the conventional HEMT structure introduces a reduction in the tension of the AlGaN barrier, which results in an improvement of the surface morphology (0.46 nm). As a consequence, the two-dimensional electron gas (2DEG) mobility increases by remarkable 46% (1900 cm 2 V À1 s À1). The HLHT AlN buffer, substituting for the HT AlN buffer, leads to the enhancement of GaN crystalline quality, which contributes to the performance improvement for HEMTs. The advanced HEMT, using both an AlN IL and an HLHT AlN buffer, produces increases in the DC maximum drain current by 35.5% ($680 A mm À1), and in the transconductance by 15% (114 mS mm À1) in comparison with the normal HEMT with an AlN buffer. The very low leakage current in the advanced HEMTs is caused by optimizing the design of the buffer and modifying growth parameters. Lastly, the reduction of AlGaN barrier tensile strain by inserting the HT AlN IL is promising for an improvement in AlGaN/GaN HEMT reliability.

2012 10th IEEE International Conference on Semiconductor Electronics (ICSE), 2012

ECS Transactions, 2013

We present the effect of multiple AlN buffer layers on characterizations of GaN film quality, whi... more We present the effect of multiple AlN buffer layers on characterizations of GaN film quality, which includes a thin high-low-high- temperature (HLHT) AlN buffer layers. The study is based on two different thicknesses of the GaN films on the buffers and found that the HLHT AlN buffer layers could significantly affect on the GaN films qualities. The buffer plays a very important role for the growth of GaN film on Si (111) substrate. The GaN film with an uniformly faceted surface and very high quality has been obtained at the optimized multiple HLHT AlN buffer layers of 50-nm-thick at 1010-800-1010 0C.

2014 IEEE International Conference on Semiconductor Electronics (ICSE2014), 2014

The influence of TMAl preflow to the AlN buffer layer and GaN thin film was studied by Optical Mi... more The influence of TMAl preflow to the AlN buffer layer and GaN thin film was studied by Optical Microscope, Atomic Force Microscope, X-ray diffraction and Transmission Electron Microscope. Different duration of TMAl preflow lead to substantially differences of the AlN buffer layer and GaN film properties in terms of surface morphology and crystal quality. It was found without TMAl preflow the crystal quality of AlN buffer layer and GaN deteriorated due to the formation of amorphous interlayer between Si and AlN. Meltback etching and cracks was observed on the surface of GaN grown on AlN without TMAl preflow. However, overlong duration of TMAl preflow degraded the properties of AlN buffer layer and the subsequent GaN layer. GaN grown with longer TMAl preflow suffer of poor crystal quality, high density cracks and rough surface morphology. With the optimum duration of TMAl preflow, crystal quality and surface roughness of GaN can be improved.

Solar Energy Materials and Solar Cells, 2012

Electro-optic characteristics of a fabricated n-In 0.4 Ga 0.6 N/p-Si hetero-structure solar cell ... more Electro-optic characteristics of a fabricated n-In 0.4 Ga 0.6 N/p-Si hetero-structure solar cell on Si substrate with Al and ITO (or Ti/Al/Ni/Au) materials for p and n-type contacts were investigated in this letter. The solar cell devices with ITO as n-type contacts were also compared to the solar cell using Ti/Al/Ni/Au as n-type contact in this study. High short-circuit current density observed for solar cell with ITO as n-type contacts due to the increased amount of light reaching the solar cell. The device with ITO contact exhibited an open-circuit voltage (V oc) of 1.52 V and a short-circuit current density (J sc) of 8.68 mA/cm 2 with 54% fill factor. The conversion and external quantum efficiency (EQE) of the solar cell were 7.12 and 20.8%, respectively. Besides, a relationship between V oc and In content in the In x Ga 1 À x N alloys for this type of solar cell was also derived.

Modern Physics Letters B, 2011

General analytic expression for the intensity-dependent absorption coefficient (IDAC) of an inten... more General analytic expression for the intensity-dependent absorption coefficient (IDAC) of an intense electromagnetic wave (IEMW) in two-dimensional electron systems (2DES) is obtained by using the quantum kinetic equation (QKE) for electrons in the case of electron–optical phonon scattering in a doped semiconductor superlattice (DSSL). The dependence of IDAC on the amplitude E0 and the photon energy ℏΩ of an IEMW, the energy ℏωp and the temperature for a specific n-i-p-i superlattice of GaAs : Si / GaAs : Be is achieved due to a numerical method. The computational results show that not only the dependence of IDAC on ℏΩ but also the dependence of IDAC on ℏωp can be applied to optically detect the electric subbands in a DSSL.

Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2010

GaN film grown on Si substrate using multilayer AlN/AlxGa1−xN buffer is studied by the low-pressu... more GaN film grown on Si substrate using multilayer AlN/AlxGa1−xN buffer is studied by the low-pressure metal-organic chemical-vapor deposition method. The AlxGa1−xN films with Al composition varying from 1 to 0.66 were used to accommodate the stress induced between GaN and the Si substrate during GaN growth. The correlation of the Al composition in the AlxGa1−xN films with respect to the stress induced in the GaN film grown was studied using high-resolution x-ray diffraction, including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1−xN buffer layer, crack-free GaN film can be successfully grown on 6 in. Si (111) substrates using multilayer AlN and AlxGa1−xN buffer layers.

American Journal of Preventive Medicine, 2006

Background: Vietnamese-American women have the highest incidence of cervical cancer of any ethnic... more Background: Vietnamese-American women have the highest incidence of cervical cancer of any ethnic group, and they underutilize Papanicolaou (Pap) tests. Design: Development and implementation of a multifaceted intervention using community-based participatory research (CBPR) methodology and evaluated with a quasi-experimental controlled design with cross-sectional pre-intervention (2000) and post-intervention (2004) telephone surveys. Data were analyzed in 2005. Setting: Santa Clara County, California (intervention community) and Harris County, Texas (comparison community). Participants: Vietnamese-American women aged 18 and older (n ϭ1566 at pre-intervention and 2009 at post-intervention). Intervention: A community-academic coalition developed and implemented six components: Vietnamese-language media campaign, lay health worker outreach, Vietnamese Pap clinic, patient registry/reminder system, restoration of a government-funded low-cost screening program, and continuing medical education for Vietnamese physicians.

IEEE Transactions on Device and Materials Reliability, 2020

The charge trapping effects on AlGaN/GaN HEMTs under UV illumination are investigated using the p... more The charge trapping effects on AlGaN/GaN HEMTs under UV illumination are investigated using the pulsed current-voltage (I-V) measurement method. The test samples are unpassivated Schottky-gate HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) with SiN gate dielectric. For HEMTs, the dominant charge trapping sources are the surface trap states, whereas, for MIS-HEMTs, they are trap states in the SiN gate dielectric and GaN buffer. When these devices are shined with the UV light, the drain current increases apparently in both samples owing to the generated photocurrent. By combining the UV illumination and pulsed I-V measurement, we find out the UV light has less effect on the surface charge trapping in the unpassivated HEMTs. Moreover, in MIS-HEMTs, we observe the charge trapping in the SiN gate dielectric becomes more serious under UV illumination, whereas the charge trapping in the GaN buffer is suppressed significantly. These findings are important for designing a GaN-based HEMT for photonic applications. In addition, the different responses of the surface-, buffer-, and gate-dielectric-related charge trapping to the UV light suggest that it would be easier to distinguish the trap types by introducing the UV illumination during the pulse measurement.