Browsing by Author "Ho, Yen Teng"

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Barrier Strain and Carbon Incorporation-Engineered Performance Improvements for AlGaN/GaN High Electron Mobility Transistors
(2015-03-01)
Tien Tung Luong
;
Ho, Yen Teng
;
Binh Tinh Tran
;
Woong, Yuen Yee
;
Chang, Edward Yi
The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) grown using metal-organic (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 high-low-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 17V 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-1 s(-1)). 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% (similar to 680Amm(-1)), and in the transconductance by 15% (114 mSmm(-1)) 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.
Electrical Properties of Compound 2D Semiconductor Mo1-xNbxS2
(2018-01-01)
Lu, Peng
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Ho, Yen Teng
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Chu, Yung-Ching
;
Zhang, Ming
;
Chien, Po-Yen
In order for TMD such as molybdenum disulfide (MoS2) to be useful for semiconductor industry, a controllable doping process is required. MoS2 with substitutional Nb shows a p-type behavior compared to the n-type characteristics of nominal films. In this work, the role of Nb in MoS2 will be examined, and a precise hole concentration control technique is demonstrated. Multi-layered Mo1-xNbxS2 samples with accurately controlled Nb mole fraction are synthesized. Electrical characterization and material analysis are performed to quantify the impact of Nb with mole fraction from 3.5% to 11%. The effective carrier concentration (p) and the ective hole mobility (mu(eff)) are found to be highly non-linear with respect to Nb mole fraction. Scanning Tunneling Microscope (STM) shows that the bandgap of the 2D transition metal dichalcogenide (TMD) is reduced by high mole fraction Nb. Therefore, Mo1-xNbxS2 can be considered as a compound TMD semiconductor.
High performance UV photodetector based on MoS2 layers grown by pulsed laser deposition technique
(2020-09-15)
Kumar, Sujit
;
Sharma, Anjali
;
Ho, Yen Teng
;
Pandey, Akhilesh
;
Tomar, Monika
Highly efficient ultraviolet (UV) photodetector based on Molybdenum Disulfide (MoS2) layers has been fabricated using pulsed laser deposition (PLD) technique. Systematic layer dependent photoresponse studies have been performed from single layer to 10 layers of MoS2 by varying the laser pulses to see the effect of the number of layers on the photoelectrical measurements. Raman and Photoluminescence studies have been carried out to ensure the growth of high-quality MoS2 layers. Layers of MoS2 grown at 100 pulses were found to exhibit the characteristic Raman phonon modes i.e. E-2g(1) and A(1g )at 383.8 cm(-1) and 405.1 cm(-1) respectively and Photoluminescence (PL) spectra show B exciton peak for MoS2 at around 625 nm suggesting the growth of high-quality MoS2 layers. Atomic force microscopy (AFM) thickness profiling and cross sectional-high resolution transmission electron microscopy (HRTEM) analysis gives the thickness of grown MoS2 to be 2.074 nm and 1.94 nm, respectively, confirming the growth of trilayers of MoS2. X-ray photoelectron spectroscopy (XPS) spectra of the grown trilayer sample show characteristic peaks corresponding to Molybdenum and Sulphur doublet (Mo4+ 3d(5/2,3/2) and S 2p(3/2,1/2)) confirming the chemical state of pure MoS2 phase without the presence of any Molybdenum oxide state. Dynamic photoelectrical studies with Indium Tin Oxide (ITO) as contact electrode upon UV laser illumination show superior responsivity of 3 x 10(4) A/W at 24 mu W optical power of the incident laser (lambda = 365 nm) and very high detectivity of 1.81 x 10(14) Jones at a low applied bias of 2 V. The obtained results are highly encouraging for the realization of low power consumption and highly efficient UV photodetectors based on MoS2 layers. (C) 2020 Elsevier B.V. All rights reserved.