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142 results on '"Chen, H.R."'

12. Influence of oxygen on the performance of GaAs/AlGaAs quantum well infrared photodetectors

Author

Tsai, K.L., Lee, C.P., Chang, K.H., Chen, H.R., and Tsang, J.S.

Subjects
Photodetectors -- Design and construction, Oxygen -- Analysis, Photoluminescence -- Analysis, Physics
Abstract

GaAs/AlGaAs quantum well infrared photodetectors (QWIP), when treated with low oxygen concentration, demonstrated a higher performance than QWIPs treated with high oxygen concentrations. Photoluminescence and secondary ion mass spectroscopy were used to study the effect of oxygen on QWIP performance. Oxygen atoms effectively lowered the dark current and responsivity of QWIP.

Published
1994

13. Investigation of indium doping in InGaAs/GaAs/AlGaAs graded-index separated confinement heterostructure lasers

Author

Tsang, J.S., Lee, C.P., Liu, D.C., Chen, H.R., Tsai, K.L., and Tsai, C.M.

Subjects
Semiconductor doping -- Research, Gallium arsenide -- Research, Gallium arsenide semiconductors -- Research, Lasers -- Research, Physics
Abstract

Proper amount of Indium (IN) doping in the graded-index guiding layer on threshold current densities of InGaAs/GaAs strained graded-index separated confinement heterostructure quantum well (GRINSCH-QW) lasers produces a reduction in threshold current densities of the GRINSCH-QW laser. Reduction in group III vacancies which are produced by high migration rate of the Indium atoms causes a reduction of the threshold current densities. A comparison of the effects of In doping and heat treatment on laser performance shows that In doped lasers have a lower threshold current density than non-In-doped lasers.

Published
1993

14. The study of emitter thickness effect on the heterostructure emitter bipolar transistors

Author

Chen, H.R., Lee, C.P., Chang, C.Y., Tsang, J.S., and Tsai, K.L.

Subjects
Bipolar transistors -- Research, Physics
Abstract

The effect of variations of emitter thickness, from 300 to 900 angstroms, on the growth of AlGaAs/GaAs heterostructure emitter bipolar transistors is investigated. The emitter thickness effects on the current gain and offset voltage are also studied. The results show that the emitter thickness influences the current gain and offset voltage.

Published
1993

21. Fundamental mode operation of high-power InGaAs/GaAs/AlGaAs laser arrays

Author

Tsang, J.S., Liou, D.C., Tsai, K.L., Chen, H.R., Tsai, C.M., Lee, C.P., and Juang, F.Y.

Subjects
Semiconductor lasers -- Research, Physics
Abstract

The fundamental mode operation of high-power InGaAs/GaAs/AlGaAs laser arrays was investigated. The results showed that the incorporation of absorption regions in all the laser stripes, with the exception of the central one, will result in the alteration of the arrays' field distribution and the modal gains of the array supermodes, thus producing fundamental mode operation. Threshold current was normally 40 mA while maximum output power was in excess of 150 mW.

Published
1993

22. Nature of the hole states in Li-doped NiO

Author

Chen, H.R. and Harding, J.H.

Abstract

We have performed density functional calculations on Li0.125Ni0.875O using both the HSE06 hybrid functional and the density functional theory (DFT) + U method. Contrary to previous calculations, both methods show that the system is better described with the hole localized on the nickel ion (which is thus formally Ni3+) rather than in the oxygen valence band. We discuss the experimental results in the light of this finding and show that it is consistent with the available data.

Published
2012

23. Charge disproportionation and Jahn-Teller distortion in LiNiO2 and NaNiO2: A density functional theory study\ud

Author

Chen, H.R., Freeman, C.L., and Harding, J.H.

Abstract

Density functional theory calculations have been performed on three potential ground-state configurations of LiNiO2 and NaNiO2. These calculations show that, whereas NaNiO2 shows the expected cooperative Jahn-Teller distortion (and therefore a crystal structure with C2/m symmetry), LiNiO2 shows at least two possible crystal structures very close in energy (within 3 meV/f.u.): P21/c and P2/c. Moreover, one of them (P2/c) shows charge disproportionation of the (expected) Ni3+ cations into Ni2+ and Ni4+. We discuss the implications of this complex ground state for the interpretation of the available electron and neutron structure data, its electronic and complex magnetic behaviour.

Published
2011

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