Browsing by Author "Tseng, Chi-Che"

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Broadband Quantum-Dot Infrared Photodetector
(2010-07-01)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Kung, Shu-Yen
;
Lin, Shih-Yen
In this letter, we report the five-period quantum-dot infrared photodetectors (QDIPs) with a bi-stacked quantum-dot (QD) structure for a wide and relatively flat detection response ranging from 4 to 11 m with high responsivities. The bi-stacked QD structure consists of a standard InAs QD and an InGaAs-capped InAs QD layer separated by a 50-nm GaAs barrier layer. The device exhibits a wide detection window in the range of 4-11 mu m with high responsivities, which suggests that similar responsivities can be obtained for the standard QD and the InGaAs-capped QD layers in the mid-wavelength (MWIR) and long-wavelength (LWIR) infrared ranges, respectively. The results are advantageous for the development of broadband QDIPs covering MWIR and LWIR ranges based on the stacked QD structures.
Enhanced normal-incident absorption of quantum-dot infrared photodetectors with smaller quantum dots
(2008-07-01)
Tseng, Chi-Che
;
Chou, Shu-Ting
;
Chen, Yi-Hao
;
Chen, Cheng-Nan
;
Lin, Wei-Hsun
Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.
Enhancement of operation temperature of InAs/GaAs quantum-dot infrared photodetectors with hydrogen-plasma treatment
(2009-09-01)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
Postprocess hydrogen treatment is performed over fabricated ten-period InAs/GaAs quantum-dot infrared photodetectors. While keeping similar spectral responses at the same applied voltage, a reduced dark current is observed for the H-plasma-treated device, which is attributed to the suppression of surface leakage-current induced by surface damage during device processing. The significant reduction in dark current also enhanced the operation temperature of the device up to 100 K. Also observed are the smoothed-out mesa edges after the H-plasma treatment, which results in trapezoidal mesa edges. In this case, a longer propagation length in the device of the reflected incident light at the mesa edge would enhance the normal-incident absorption ratio of the H-plasma-treated device. (C) 2009 American Vacuum Society. [DOI:10.1116/1.3196781]
Influence of As on the Morphologies and Optical Characteristics of GaSb/GaAs Quantum Dots
(2011-03-01)
Tseng, Chi-Che
;
Mai, Shu-Cheng
;
Lin, Wei-Hsun
;
Wu, Shung-Yi
;
Yu, Bang-Ying
The influence of As atoms on the morphologies of GaSb quantum dots (QDs) is investigated. Without any special treatment, GaSb quantum rings (QRs) are observed in the embedded GaSb layer even when the uncapped layer reveals QD-like morphologies. With intentional As supply after the uncapped GaSb QD deposition, a QD to QR transition is observed. The phenomenon suggests that insufficient Sb atoms on the GaSb QDs would lead to the QD to QR transition as in the case of embedded GaSb layers. With extended Sb soaking time following GaSb deposition, QD structures could be well maintained for the embedded GaSb layers. A light-emitting diode operated at room temperature is fabricated based on the GaSb/GaAs QD structure. Identical peak positions in photoluminescence and electroluminescence (EL) spectra of the device show that type-II GaSb QDs are responsible for the observed EL.
Influence of As-stabilized surface on the formation of InAs/GaAs quantum dots
(2008-05-01)
Tseng, Chi-Che
;
Chou, Shu-Ting
;
Chen, Yi-Hao
;
Chung, Tung-Hsun
;
Lin, Shih-Yen
In this article, we report the growth of InAs/GaAs quantum dots (QDs) grown under different As(4)-supply procedures. The growth of the investigated samples carried out by the three procedures of As shutter always opened, As shutter initially opened, and As shutter initially closed. The samples grown by the former two approaches show a uniform QD distribution and the multiple-peak luminescence, which correspond to ground-state, first-excited-state, and second-excited-state luminescence, while that grown by the latter only shows large InAs islands. The results suggest that the As-stabilized condition at the initial stage of QD growth is very critical for the high-quality QD formation. (C) 2008 American Vacuum Society.
InGaAs-Capped InAs-GaAs Quantum-Dot Infrared Photodetectors Operating in the Long-Wavelength Infrared Range
(2009-09-15)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Mai, Shu-Cheng
;
Lin, Shih-Yen
A ten-period InAs-GaAs quantum-dot infrared photodetector (QDIP) with 8-nm In(0.15)Ga(0.85) As capping layer grown after quantum-dot (QD) deposition is investigated. With reduced InAs QD coverage down to 2.0 mono-layers, responses at 10.4 and 8.4 mu m are observed for the device under positive and negative biases, respectively. The phenomenon is attributed to the large Stark effect resulted from the asymmetric band diagrams of the device under different voltage polarities. The demonstration of long-wavelength infrared detections with the simple structures of the InGaAs-capped QDIP is advantageous for the development of multicolor QDIP focal-plane arrays.
Room-temperature operation type-II GaSb/GaAs quantum-dot infrared light-emitting diode
(2010-03-22)
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Lin, Wei-Hsun
;
Mai, Shu-Cheng
;
Wu, Shung-Yi
A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED.
Single-Period InAs-GaAs Quantum-Dot Infrared Photodetectors
(2008-09-01)
Chou, Shu-Ting
;
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Chen, Yi-Hao
;
Chen, Cheng-Nan
In this letter, we investigate the performance of single-period InAs-GaAs quantum-dot (QD) infrared photodetectors, in which the single-period QD is sandwiched by different thicknesses of the undoped GaAs confinement layers. By using a 5-nm p-type GaAs layer as a current blocking barrier, the investigated three devices exhibit no response. the highest response, and the medium response, respectively. It is attributed to three different electron occupancy situations in the QD region resulted from the various locations of the Fermi level. A higher barrier for the thermionic emission current is observed for the device with a lower Fermi level in the QD structure. It is attributed to the acceptor-like behavior of the depleted QD such that a higher barrier height would be observed.
Site-controlled self-assembled InAs quantum dots grown on GaAs substrates
(2010-07-23)
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Chung, Tung-Hsun
;
Liao, Wen-Hsuan
;
Chen, Shu-Han
Atomically-flat surfaces are obtained after thin GaAsSb buffer layer growth on GaAs substrates with regular-distributed nano-holes formed after oxide desorption of the local atomic-force-microscopy anode oxidation. Different from the samples with GaAsSb buffer layers, increasing surface root-mean-square roughness is observed for the GaAs-buffered samples with increasing GaAs buffer layer thickness. The phenomenon is attributed to the enhanced adatom migration resulting from the incorporation of Sb atoms. By using the substrates with nano-holes after buffer layer growth, site-controlled self-assembled InAs quantum dots (QDs) are observed with the deposition of a below-critical-thickness InAs coverage of 1.3 monolayer (ML).
The influence of background As on GaSb/GaAs quantum dots and its application in infrared photodetectors
(2012)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Wu, Shung-Yi
;
Wu, Meng-Hsun
;
Lin, Shih-Yen
In this paper, GaSb nanostructures prepared under different Sb/background As ratios are investigated. With decreasing Sb/background As ratios, the morphologies of GaSb nanostructure changing from quantum dots (QDs) to quantum rings (QRs) are observed. The higher optical recombination probabilities of GaSb QRs are attributed to enhanced electron-hole wave function overlapping and more surrounding electrons around the GaSb QR core shell. With well-control Sb/background As ratios, the high-temperature operation GaSb quantum-dot infrared photodetector (QDIP) with simple stacked structure has been demonstrated. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
The influence of In composition on InGaAs-capped InAs/GaAs quantum-dot infrared photodetectors
(2009-09-01)
Lin, Wei-Hsun
;
Chao, Kuang-Ping
;
Tseng, Chi-Che
;
Mai, Shu-Cheng
;
Lin, Shih-Yen
The influence of an additional InGaAs-capped layer on the performance of InAs/GaAs quantum-dot infrared photodetectors (QDIPs) is investigated. For the device with a 15% InGaAs-capped layer, a significant response at 7.9 mu m is observed for the QDIP device. The results suggest that with the additional InGaAs-capped layer, the detection wavelengths of the InAs/GaAs QDIPs could be shifted to a longer-wavelength infrared range. A further increase in the In composition will not help to obtain an even longer-wavelength detection, which is attributed to the cancellation of a lower InGaAs state, and InAs-QD bandgap shrinkage resulted from the relaxed compressive strains of the InGaAs layer with a higher In composition.
The transition mechanisms of a ten-period InAs/GaAs quantum-dot infrared photodetector
(2008-11-01)
Tseng, Chi-Che
;
Chou, Shu-Ting
;
Lin, Shin-Yen
;
Chen, Cheng-Nan
;
Lin, Wei-Hsun
This study explores the growth and effects of a ten-period InAs/GaAs quantum-dot infrared photodetector (QDIP). With a uniform quantum-dot (QD) size distribution and a QD density of 2.8x10(10) cm(-2), this 10 K photoluminescence spectrum shows a peak energy at 1.07 eV and a narrow full width at half maximum of 31.7 meV. The QDIP exhibits an asymmetric response under different voltage polarities and a high responsivity of 1.7 A/W at -1.1 V. Another noticeable observation in the spectral response of the device is the 6 mu m peak detection wavelength with a high spectral broadening Delta lambda/lambda of 0.67. By analyses of the photoluminescence excitation spectrum and the temperature dependence of spectral response, the wide spectral response of the QDIP is attributed to the summation of transitions between QD excited states and the wetting layer states, instead of transitions between QD ground state and higher excited states.
The transition mechanisms of type-II GaSb/GaAs quantum-dot infrared light-emitting diodes
(2011-05-15)
Tseng, Chi-Che
;
Lin, Wei-Hsun
;
Wu, Shung-Yi
;
Chen, Shu-Han
;
Lin, Shih-Yen
The light-emitting diode (LED) with a single GaSb QD layer embedded in a GaAs n-i-p structure operated under different injection currents and temperatures is investigated. With increase in injection currents, room-temperature electroluminescence (EL) peak blue shift is observed until a saturation of EL intensity is reached. In the temperature-varying EL measurements, with increase in temperatures. EL peak blue shift and then red shift are observed, which is attributed to the enhanced luminescence of the smaller QDs with increase in temperatures lower than 100 K. The understanding of the operation mechanisms for the device is advantageous for the practical application of type-II LEDs. (C) 2010 Elsevier B.V. All rights reserved.
Transition mechanism of InAs/GaAs quantum-dot infrared photodetectors with different InAs coverages
(2010-05-01)
Tseng, Chi-Che
;
Chung, Tung-Hsun
;
Mai, Shu-Cheng
;
Chao, Kuang-Ping
;
Lin, Wei-Hsun
In this article, the authors investigate the influences of different InAs coverages on the photoluminescence excitation (PLE) spectra and spectral responses of InAs/GaAs quantum-dot infrared photodetectors (QDIPs). An increase in InAs coverage would lead to an increase in energy separation between heavy-hole state and light-hole state in the wetting layer (WL) region in the QD PLE spectra. The results suggest that most of the strain resulted from the InAs/GaAs lattice mismatch may be accumulated in the WL instead of the QD region. Also observed are the similar energy separations of energy levels responsible for the intraband absorption in the PLE spectra of the QDIPs such that similar detection wavelengths are observed for the devices. [DOI:10.1116/1.3368607]
Voltage-tunable two-color quantum-dot infrared photodetectors
(2009-09-21)
Lin, Shih-Yen
;
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Mai, Shu-Cheng
A two-terminal quantum-dot infrared photodetector with stacked five-period InAs/GaAs and InGaAs-capped InAs/GaAs quantum-dot (QD) structures is investigated. The device has exhibited distinct responses at mid-wavelength and long-wavelength infrared regions under positive and negative biases, respectively. The results suggest that the QD confinement states near the anode side are completely filled, such that selective responses at different wavelength ranges would be observed for the stacked structure under different voltage polarities. Also observed are the similar absorption ratios of the device under different incident light polarizations at the two response regions. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3236543]
Wavelength-Tunable InGaAs-Capped Quantum-Dot Infrared Photodetectors
(2010-02-15)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Mai, Shu-Cheng
;
Lin, Shih-Yen
Quantum-dot infrared photodetectors (QDIPs) with InGaAs capping layers are investigated. Compared with the standard QDIP with 2.5-mono-layer (ML) InAs QDs, the detection wavelength is shifted from 6 to 7.9 m for an 8-nm InGaAs-capped QDIP. By decreasing the QD coverage from 2.5 to 2.0 ML, an even longer detection wavelength 10.4 m is observed, which is attributed to the higher energy levels of the QD excited states resulted from the smaller QDs. By further increasing the capping layer thickness to 12 nm, longer detection wavelengths with broad response 10-18 m is observed for the InGaAs-capped QDIP.
Wavelength-tunable InGaAs-capped quantum-dot infrared photodetectors for multi-color detection
(2011-05-01)
Lin, Wei-Hsun
;
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Kung, Shu-Yen
;
Chao, Kuang-Ping
A two-terminal quantum-dot infrared photodetector (QDIP) with stacked 5-period InAs/GaAs and InGaAs-capped InAs/GaAs QD structures is investigated in this paper. The device has exhibited distinct responses at mid-wavelength and long-wavelength infrared regions under positive and negative biases, respectively. Also observed for the device are the equal normal absorption ratios under different voltage biases for the device under either MWIR or LWIR ranges. The device has revealed its potential in the application of voltage-tunable and multi-color detections. (C) 2010 Elsevier B.V. All rights reserved.