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Author

M. Happ

Bio: M. Happ is an academic researcher. The author has contributed to research in topics: Electronic band structure & Band gap. The author has an hindex of 1, co-authored 1 publications receiving 16 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a semi-empirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model.
Abstract: A semiempirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model. This model correctly fits both the absorption and luminescence spectra of narrow‐gap (Hg,Cd)Te samples that have been grown by the traveling heater method as well as by molecular‐beam epitaxy. The accuracy of the band‐gap determination is enhanced by this model.

16 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the successive steps for realizing dual-band infrared detectors operating in the mid-wavelength infrared (MWIR) band were presented, where high crystalline quality HgCdTe multilayer stacks have been grown by molecular beam epitaxy (MBE) on CdZnTe and CdTe/Ge substrates.
Abstract: In this paper, we present all the successive steps for realizing dual-band infrared detectors operating in the mid-wavelength infrared (MWIR) band. High crystalline quality HgCdTe multilayer stacks have been grown by molecular beam epitaxy (MBE) on CdZnTe and CdTe/Ge substrates. Material characterization in the light of high-resolution x-ray diffraction (HRXRD) results and dislocation density measurements are exposed in detail. These characterizations show some striking differences between structures grown on the two kinds of substrates. Device processing and readout circuit for 128×128 focal-plane array (FPA) fabrication are described. The electro-optical characteristics of the devices show that devices grown on Ge match those grown on CdZnTe substrates in terms of responsivity, noise measurements, and operability.

29 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of optical absorption due to interband transitions in direct-gap semiconductors is revisited, and an analytical expression for the linear absorption coefficient in narrow-gap ICs is obtained by including the nonparabolic band structure due to Keldysh [Sov. Phys. 6, 763 (1958)] and Burstein-Moss shift.
Abstract: The theory of optical absorption due to interband transitions in direct-gap semiconductors is revisited. An analytical expression for the linear absorption coefficient in narrow-gap semiconductors is obtained by including the nonparabolic band structure due to Keldysh [Sov. Phys.–JETP 6, 763 (1958)] and Burstein–Moss shift. Numerical results are obtained for Hg1−xCdxTe for several values of x and temperature, and compared with recent experimental data. The agreement is found to be good.

18 citations

Journal ArticleDOI
Biao Li1, J.H. Chu1, Yia-Chung Chang1, Y.S. Gui1, D.Y. Tang1 
TL;DR: Based on the intrinsic absorption spectra of Hg 1- x Cd x Te performed on thin films of thin Hg1-x Cdx Te bulk material with x ranging from 0.170 to 0.443 and at temperatures from 4.2 to 300 K, the expressions for the intrinsic optical absorption coefficient in the Kane region are reviewed as mentioned in this paper.

15 citations

Journal ArticleDOI
TL;DR: In this article, a series of annealed narrow-gap Hg1−xCdxTe (0.3 < x < 0.4) crystals grown by the travelling heater method (THM) were studied in order to get insight in the action of many-body effects (band gap renormalization, free excitons and their localization).

11 citations

DissertationDOI
03 Nov 2004
TL;DR: In this paper, the effect of device scaling on device characteristics like noise and absolute magnetic sensitivity is studied, where the authors show that a thick pseudomorphically strained InGaAs layer causes not only a higher absolute magnetic sensitivities and a better thermal stability, but also lower 1/f noise being a result of conductivity fluctuations.
Abstract: Doped-channel quantum well (QW) AlGaAs/GaAs and AlGaAs/GaAs/InGaAs as well as modulation-doped AlGaAs/InGaAs/GaAs heterostructures based on high electron drift velocity semiconductors are successfully applied to the fabrication of micro-Hall devices. Considering these devices as magnetic sensors, their properties were characterized in terms of signal linearity, sensitivity and noise at low and high electric fields. Even at electric fields higher than 1.8 kV · cm−1, the doped-channel devices exhibit an excellent signal linearity. Magnetic sensitivities up to 600 V ·A−1 ·T−1 in current drive mode are measured. The usage of a Si-δ-doped pseudomorphic InGaAs QW results in better sensitivity and noise performance than does uniformly doped GaAs. A maximal signal-to-noise sensitivity (SNS) of 138 dB ·T−1 is achieved in a 10 μm square size device at 300 K, 100 kHz frequency and 1 Hz bandwidth. Because the performance in these structures is driven in part by the high electron drift velocity, it does not degrade even at high electric fields up to 2.4 kV ·cm−1 and corresponds to a lowest detection limit of 127 nT·Hz−1/2. Comparatively, the modulation-doped devices of 20 μm square size exhibit a higher SNS of 141 dB · T−1 at low electric fields, but degrade at higher fields. Thus, the doped-channel pseudomorphically strained InGaAs QW high-velocity devices have several advantages over modulation-doped high-mobility structures at high electric fields. Thermal stability studies of doped-channel QW devices reveal a thick InGaAs layer (within a fixed total thickness of the GaAs/InGaAs channel) necessary to avoid the parasitic parallel conductivity in GaAs channel. Using this result and a high doping level, superior temperature stabilities of 90 ppm ·K−1 in the current drive mode and 192 ppm · K−1 in the voltage drive mode are attained. Independently, optical studies like photoluminescence and Raman scattering reveal a high degree of disorder in thin InGaAs QWs, being negligible for thick pseudomorphic InGaAs layers. Hence, a thick InGaAs layer causes not only a higher absolute magnetic sensitivity and a better thermal stability, but also lower 1/f noise being a result of conductivity fluctuations. Special effort is devoted to the application of deep level noise spectroscopy as a very sensitive probe for semiconductor bulk and layer quality. Combined with supply-current-related sensitivity studies, this method is most suitable for micro-Hall device optimization. The effect of device scaling on device characteristics like noise and absolute magnetic sensitivity is studied. Both the SNS and detection limit are shown as size-dependent. Additionally, geometry effects on the electric field distribution for Greek cross shapes are simulated by numerical calculations and discussed. Rounded corners appear as most appropriate for the fabrication of highly sensitive low-noise micro-Hall devices.

7 citations