Height-selective etching for regrowth of self-aligned contacts using MBE
Advanced III-V transistors require unprecedented low-resistance contacts in order to simultaneously scale bandwidth, f max and f t with the physical active region [M.J.W. Rodwell, M. Le, B. Brar, in: Proceedings of the IEEE, 96, 2008, p. 748]. Low-resistance contacts have been previously demonstrated using molecular beam epitaxy (MBE), which provides active doping above 4 x 10 19 cm -3 and permits in-situ metal deposition for the lowest resistances [U. Singisetti, M.A. Wistey, J.D. Zimmerman, B.J. Thibeault, M.J.W. Rodwell, A.C. Gossard, S.R. Bank, Appl. Phys. Lett., submitted]. But MBE is a blanket deposition technique, and applying MBE regrowth to deep-submicron lateral device dimensions is difficult even with advanced lithography techniques. We present a simple method for selectively etching undesired regrowth from the gate or mesa of a III-V MOSFET or laser, resulting in self-aligned source/drain contacts regardless of the device dimensions. This turns MBE into an effectively selective area growth technique.
High Performance 1.55 μm InGaAsP Buried-Heterostructure Laser Diodes Fabricated by Single-Step MOCVD Regrowth and Self-Aligned Technique
In this article, we demonstrate a simple and low-cost method to fabricate the 1.55 μm strained multiquantum-well InGaAsP/InP buried-heterostructure (BH) laser diodes (LDs) by using the single-step metallorganic-chemical-vapor-deposition (MOCVD) regrowth and self-aligned technique. The active region is buried by the intrinsic InP layer which is used as the current-blocking layer as well as the electrical and optical confinement layer. The BH LDs have a calculated internal quantum efficiency of 81% and an internal loss of 21.5 cm -1 . The fabricated as-cleaved BH LDs exhibit a threshold current of 6.5 mA, a maximum light output power of 21 mW at 100 mA, a maximum operating temperature of 100°C, and a characteristic temperature of 72 K in 20-60°C. The BH LDs with an as-cleaved front facet and a high reflectivity coating (∼92%) applied to the rear facet can increase the maximum operation temperature up to 125°C and have a light output power exceeding 10 mW at 80 mA and 100°C. The 3 dB frequency at a bias current of 40 mA is 8.0, 6.5, and 5.2 GHz at 30, 60, and 90°C, respectively. Besides, the 3 dB modulation bandwidth can be extended as far as 10.5 GHz at 20°C and 60 mA. These results confirm that BH LDs have the potential capacity for high-speed fiber optic applications.
Techno-economic analysis of chemical looping combustion with humid air turbine power cycle
Abstract Power generation from fossil fuel-fired power plant is the largest single source of CO2 emission. CO2 emission contributes to climate change. On the other hand, renewable energy is hindered by complex constraints in dealing with large scale application and high price. Power generation from fossil fuels with CO2 capture is therefore necessary to meet the increasing energy demand, and reduce the emission of CO2. This paper presents a process simulation and economic analysis of the chemical looping combustion (CLC) integrated with humid air turbine (HAT) cycle for natural gas-fired power plant with CO2 capture. The study shows that the CLC–HAT including CO2 capture has a thermal efficiency of 57% at oxidizing temperature of 1200 °C and reducer inlet temperature of 530 °C. The economic evaluation shows that the 50 MWth plant with a projected lifetime of 30 years will have a payback period of 7 years and 6 years for conventional HAT and CLC–HAT cycles respectively. The analysis indicates that CLC–HAT process has a high potential to be commercialised.