Browsing by Author "Yen, Shun-Tung"

Now showing 1 - 15 of 15

Analysis of GaAs/GaSb/GaAs structures under optical excitation considering surface states as an electron reservoir
(2009-05-15)
Hsieh, Hong-Wen
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present a self-consistent model for the analysis of the carrier distribution, the band profile, and the transition energy of type-II aligned GaAs/GaSb/GaAs structures under optical excitation. The model considers the surface states as an electron reservoir, associated with pinning of the conduction band Fermi level at the midgap. In our model, the optical generated holes in the GaSb quantum well causes a potential well on one side of the GaSb layer, which can efficiently accommodate the optically generated electrons. Accordingly, we derive a relation connecting the excitation power to the carrier density. Using the relation and the effective triangular potential approximation, we obtain a simple formula for the transition energy shift as a function of the excitation power, which follows the cube-root rule quite well. The calculation allows the determination of the band offset of a type-II heterointerface by comparison with data from photoluminescence measurement. The result suggests the unstrained valence band offset of GaSb/GaAs to lie between 0.5 and 0.55 eV. We also present a simplified model for analyzing the electronic and optical properties of type-II heterostructures without the need of a self-consistent calculation.
Analysis of GaAs/GaSb/GaAs structures under optical excitation considering surface states as an electron reservoir (vol 105, 103515, 2009)
(2009-06-15)
Hsieh, Hong-Wen
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Analysis of heterostructures for electroluminescent refrigeration and light emitting without heat generation
(2010-03-01)
Yen, Shun-Tung
;
Lee, Kuan-Chen
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We perform a self-consistent calculation to investigate the feasibility of electroluminescent refrigeration and light emitting without heat generation in AlGaAs/GaAs heterostructures, taking into account the effects of various recombination processes. The effect of radiation extraction on the cooling capacity and efficiency is also considered. Carrier blocking layers are used to almost eliminate current leakage and improve the injection efficiency to nearly 100%. An analysis is presented of the cooling power density, the cooling efficiency, and the radiative power density as functions of the applied voltage. We also explore the dependences of the cooling related quantities on the thickness and the doping of the active region. A GaAs active layer of thickness 5 mu m at 300 K can give a limiting cooling power density of 97 W/cm(2). We show that a net cooling power (>several W/cm(2)) and a high-power light emitting (>100 W/cm(2)) without heating are feasible. They require an overall efficiency of more than 90%, which is easily achieved if the photon recycling efficiency is high. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3326944]
Analysis of two-phonon infrared spectral features of gallium arsenide and indium phosphide by first-principles calculations
(2014-12)
Lin, Huang-Hsiang
;
Chung, Pei-Kang
;
Yen, Shun-Tung
;
電機學院
;
電子工程學系及電子研究所
We perform a self-consistent calculation based on density functional perturbation theory to analyze the infrared spectral features of GaAs and InP arising from two-phonon processes. The features are identified and assigned the critical points in the first Brillouin zone. Distribution of the critical points is investigated. The analysis demonstrates that collections of phonons of wave vectors around symmetry points and along symmetry lines are responsible for strong infrared features in two-phonon processes.
Discrete monolayer light emission from GaSb wetting layer in GaAs
(2007-06-11)
Lo, Ming-Cheng
;
Huang, Shyh-Jer
;
Lee, Chien-Ping
;
Lin, Sheng-Di
;
Yen, Shun-Tung
Distinct light emission peaks from monolayers of GaSb quantum wells in GaAs were observed. Discrete atomic layers of GaSb for the wetting layer prior to quantum dot formation give rise to transition peaks corresponding to quantum wells with 1, 2, and 3 ML. From the transition energies the authors were able to deduce the band offset parameter between GaSb and GaAs. By fitting the experimental data with the theoretical calculated result using an 8x8 k center dot p Burt's Hamiltonian along with the Bir-Picus deformation potentials, the strain-free (fully strained) valence band discontinuity for this type-II heterojunction was determined to be 0.45 eV (0.66 eV). (c) 2007 American Institute of Physics.
Efficient far-infrared thermal bremsstrahlung radiation from a heterojunction bipolar transistor
(2015-08-28)
Chung, Pei-Kang
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We investigate the far-infrared thermal radiation properties of a heterojunction bipolar transistor. The device conveniently provides a high electric field for electrons to heat the lattice and the electron gas in a background with ions embedded. Because of very high effective temperature of the electron gas in the collector, the electron-ion bremsstrahlung makes efficient the thermal radiation in the far-infrared region. The transistor can yield a radiation power of 0.1 mW with the spectral region between 2 and 75 THz and a power conversion efficiency of 6 x 10(-4). Such output contains a power of 20 mu W in the low-frequency part (2-20 THz) of the spectrum. (C) 2015 AIP Publishing LLC.
Electron spillover effects in InGaN/GaN quantum-well lasers
(2007-12-01)
Huang, Shyh-Jer
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effects of electron spillover from quantum wells on the optical property of InGaN/GaN laser diodes are theoretically studied in detail. A six-band model including strain effects is used to calculate valence band states. Continuous subbands unconfined to the quantum wells are simulated deliberately by densely discretized subbands for the spillover electrons. The calculation results show obvious differences in the radiative current densities and the gain spectra between the cases with and without considering the spillover effect. We further investigate the spillover effect on the radiative current densities and the spontaneous emission spectra, with variations in the depth and the width of quantum wells, the total loss of the cavity, and the temperature. For shallow wells, the spillover effect is particularly important. It broadens both the gain and the spontaneous emission spectra and hence deteriorates the threshold of laser diodes. Such an effect can be alleviated by employing a long cavity and a multi-quantum-well active region. The concept of the electron spillover studied in this work is not only applicable to the nitride lasers but also to other kinds of quantum-well lasers. (C) 2007 American Institute of Physics.
Enhanced thermal radiation in terahertz and far-infrared regime by hot phonon excitation in a field effect transistor
(2014-11-14)
Chung, Pei-Kang
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We demonstrate the hot phonon effect on thermal radiation in the terahertz and far-infrared regime. A pseudomorphic high electron mobility transistor is used for efficiently exciting hot phonons. Boosting the hot phonon population can enhance the efficiency of thermal radiation. The transistor can yield at least a radiation power of 13 mu W and a power conversion efficiency higher than a resistor by more than 20%. (C) 2014 AIP Publishing LLC.
Extraction of eight-band k . p parameters from empirical pseudopotentials for GeSn
(2019-06-28)
Liu, Shao-Qi
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We extract the parameters for the eight-band k . p model for Ge 1 - x Sn x ( x <= 0.15 ) from the calculation of the nonlocal empirical pseudopotential method with the modified virtual crystal approximation. The atomic pseudopotential form factors of Ge are improved such that the calculated Ge band structure has the commonly accepted bandgap and effective masses. The improved Ge parameters are used in proper interpolation to derive the parameters of GeSn for empirical pseudopotential calculation. The calculated band structures suggest that the Ge 1 - x Sn x alloys exhibit a transition between an indirect bandgap semiconductor and a direct one at Sn composition x c = 0.071. From the calculation, we extract the bandgap, the split-off energy, the interband momentum matrix element, and the effective masses of Ge 1 - x Sn x ( x <= 0.15) as functions of x. From these results, we further derive the parameters used in the eight-band k . p model. These parameters are well expressed in quadratic form. The k . p model with the extracted parameters can give an interband tunneling current in a pin diode that is consistent with the current calculated by the empirical pseudopotential method.
Extraction of infrared optical constants from fringing reflectance spectra
(2014-10-21)
Chung, Pei-Kang
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We propose a simple and reliable method for extracting the optical constants of homogeneous dielectrics which can be pure or impure, and polar or nonpolar. The extraction is made from fringing reflectance spectra of slab samples with and without metal on the backside. The method is demonstrated to work well for polar semiconductors GaAs and InP in the infrared regime. The extracted extinction coefficient spectra exhibit plenty of features which correspond well to those in absorption and Raman spectra. (C) 2014 AIP Publishing LLC.
Extraction of optical constants from maxima of fringing reflectance spectra
(2015-02-01)
Yen, Shun-Tung
;
Chung, Pei-Kang
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We propose a scheme to extract the refractive index and the extinction coefficient of dielectrics. The extraction needs only a reflectance spectrum with reliable successive maxima of fringing oscillations measured from a dielectric film that is either freestanding or on metal. With the film thickness known in advance, we determine the refractive index spectrum from the fringing oscillation periods and then the extinction coefficient spectrum from the upper envelope. The method is demonstrated to work well for GaAs and Ge. (C) 2015 Optical Society of America
Far-infrared quasi-monochromatic perfect absorption in a thin GaAs film on gold
(2015-08-15)
Yen, Shun-Tung
;
Chung, Pei-Kang
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We study the far-infrared absorption properties of a thin GaAs film on Au. We show that a 1.2-mu m GaAs film on Au can completely absorb an electromagnetic wave of 7.9 THz and totally reflect the waves of frequencies not very close to 7.9 THz. The uniformity of the layered structure enables observation of a quasi-monochromatic, nearly perfect absorption of 96% in a 1.4-mu m GaAs film. The absorption can be high for a wide range of incident angles. (C) 2015 Optical Society of America
Improvement in threshold of InGaN/GaN quantum-well lasers by p-type modulation doping
(2007-12-01)
Huang, Shyh-Jer
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The optical properties of modulation-doped InGaN/GaN laser diodes are theoretically studied with the effects of electron spillover from quantum wells considered. We use a six-band model including the strain effect for calculating valence band states. The continuous subbands are treated by a dense discretization for the electrons spilling from the quantum wells. The calculation results show that the threshold current can be significantly reduced by p-type modulation doping around the wells but not by n-type doping, supposed that the layers are of a perfect quality and the impurity-induced defects are ignored. Also, the p-type modulation doping can make the threshold current more insensitive to the cavity loss compared with other cases. An optimized threshold current density can be achieved for single-quantum-well lasers by introducing p-type dopants. However, the dopant concentration is high and may be inaccessible. For double-quantum-well lasers an optimized low threshold current can be achieved with a slighter and practicable p-type doping level. (C) 2007 American Institute of Physics.
Optical properties and potential applications of epsilon-GaSe at terahertz frequencies
(2009-09-01)
Chen, Ching-Wei
;
Tang, Tsung-Ta
;
Lin, Sung-Hui
;
Huang, Jung Y.
;
Chang, Chen-Shiung
Ordinary and extraordinary refractive indices of an epsilon-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOM similar to 10(3) at 1 THz), the large birefringence (Delta n similar to 0.76 at 1 THz). and the low absorption coefficient (alpha similar to 0.2 cm(-1) at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed. (C) 2009 Optical Society of America
Photon recycling effect on electroluminescent refrigeration
(2012-01-01)
Lee, Kuan-Chen
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We study electroluminescent refrigeration in an AlGaAs/GaAs double heterostructure by a self-consistent calculation with photon recycling considered. To gain insight, we investigate the influence of the recycling on the carrier density and the current components due to various recombination mechanisms in the device under different bias voltages. The photon recycling is a feedback process, which behaves as an internal source of generating electron-hole pairs in the active region and causes an effective feedback current to compensate the driving current from the external source. Consequently, it reduces the driving current, improves the external quantum efficiency, and loosens the requirement on the photon extraction efficiency for refrigeration. For the device with a 1 mu m GaAs active layer operating at 300 K, the minimum required extraction efficiency is less than 20% if the trapped photons are completely recycled and remains a feasible value of 45% if the recycling efficiency is 90%, which is not difficult to achieve. In addition, photon recycling eases the problem of the drastic deterioration of the cooling power and the external efficiency as the extraction efficiency reduces. These results reveal a good possibility of realizing electroluminescent refrigeration in semiconductors. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676249]