Browsing by Author "Hsieh, WH"

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High-sensitivity microwave vector detection at extremely low-power levels for low-dimensional electron systems
(2004-11-01)
Hsieh, WH
;
Kuan, CH
;
Suen, YW
;
Chang, SY
;
Li, LC
We present a high-sensitivity microwave vector detection system for studying the low-dimensional electron system embedded in the gaps of a coplanar waveguide at low temperatures. Using this system, we have achieved 0.005% and 0.001degrees resolutions in amplitude and phase variations, respectively, at 10 GHz in a magnetotransport measurement on a quantum-wire array with an average signal power less than -75 dBm into the sample at 0.3 K. From the measured phase variation, we can distinguish a very tiny change in the induced dipole moment of each quantum wire. (C) 2004 American Institute of Physics.
Performance and application of a superlattice infrared photodetector with a blocking barrier
(2002-02-01)
Chen, CC
;
Chen, HC
;
Hsu, MC
;
Hsieh, WH
;
Kuan, CH
An infrared photodetector that contains a superlattice structure and a blocking barrier was investigated. The photodetector shows advantages including a low operating voltage (<0.7 V), wide detection bandwidth, flexible miniband engineering, and in particular, voltage-tunable spectral responsivity. The blocking barrier not only prohibits the dark current but also acts as a high-pass energy filter to tune the spectral responsivity. The zero background peak detectivity of our detector is 3.7x10(9) cm Hz(0.5)/W (9.7 mum) at -0.5 V and 2.2x10(10) cm Hz(0.5)/W (6.7 mum) at -0.1 V. Since the spectral responsivity at different biases is independent, temperature sensing is feasible by taking the ratio of the measured photocurrent at different biases. A demonstration of temperature sensing by using our superlattice infrared photodetector with a blocking barrier is also shown in this article. Those results show the superlattice is a simple and efficient structure for the design of a multicolor infrared photodetector. (C) 2002 American Institute of Physics.
Relaxation mechanisms of the photoelectrons in the second miniband of a superlattice structure
(2003-02-01)
Chen, CC
;
Chen, HC
;
Hsu, MC
;
Hsieh, WH
;
Kuan, CH
Photoelectron relaxation in the second miniband of a superlattice was studied with a high-pass energy filter at one end of the superlattice. By analyzing the spectral responses with different biases across the energy filter, the photoelectron distribution and relaxation in the second miniband of the superlattice can be resolved. In this paper, a model based on the rate equation is proposed to extract the related parameters of the photoelectron transport. The photoelectrons suffer from both intraminiband and interminiband relaxation. The extracted interminiband relaxation time is 11 ps, while the intraminiband one is in the sulipicosecond range. In addition, this structure can also be utilized as an infrared photodetector. Our analysis shows that the fast intraminiband relaxation is the dominant mechanism of the maximum achievable responsivity of the detector and the theoretical model not only provides the insight of the photoelectron transport in the superlattice miniband but also is useful for designing a superlattice infrared photodetector.
Self-assembled GaAs antiwires in In0.53Ga0.47As matrix on (100) InP substrates
(2002-10-14)
Lin, SD
;
Lee, CP
;
Hsieh, WH
;
Suen, YW
;
電子工程學系及電子研究所
The growth of GaAs antiwires in the In0.53Ga0.47As matrix on InP substrate has been investigated. The periodic, wire-like structure was obtained when a proper amount of GaAs was deposited. The grown antiwires have a height about 1.2-2.0 nm and a period about 23 nm. Using an In0.53Ga0.47As/In0.52Al0.48As modulation-doped structure, the effect of the GaAs antiwires on the two-dimensional electron gas mobility was investigated. For the sample with antiwires near the two-dimensional channel, a significant anisotropy in low temperature mobility was observed. (C) 2002 American Institute of Physics.