Browsing by Author "Chen, Cheng-Nan"

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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.
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.
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.