Engineering topics

Shih, H. D.

Publications and source records attributed to Shih, H. D..

5 records

NASA NTRS1993

Effect of disorder on the optical properties of short period superlattices

The optical properties of disordered short period superlattices are studied using a one-dimensional tight-binding model. A difference vector and disorder structure factor are proposed to characterize the disordered superlattice. The density of states, participation number, and optical absorption coefficients for both ordered and disordered superlattices are calculated as a function of energy. The results show that introduction of disorder into an indirect band gap material enhances the optical transition near the indirect band edge.

Strozier, J. A.↗

NASA NTRS1992

Localization in one-dimensional random superlattices

The localization of electrons in intentionally disordered superlattices is simulated. By studying the density of states and the localization length, significant variation of the degree of localization is found with the type of random stacking sequence is found. It is predicted that more enhancement of luminescence can be achieved with new types or stacking sequences.

Su, W. P.↗

NASA NTRS1992

Reflection high-energy electron diffraction study of growth and interface formation of the Ga(1-x)In(x)Sb/InAs strained-layer superlattices

Reflection high-energy electron diffraction (RHEED) during molecular beam epitaxy is used to study the growth and interface formation of the Ga(1-x)In(x)Sb/InAs (x is not greater than 0.4) strained-layer superlattices (SLSs) on GaSb(100) substrates. A number of surface atomic structures were observed in the growth of the SLS: a (1 x 3) phase from the InAs epilayer surface, a (2 x 3) phase, a (2 x 4) phase, and diffuse (1 x 1)-like phases from the InAs epilayer surface. It is suggested that the long-range order quality of the interface of Ga(1-x)In(x)Sb on InAs may be better than that of the interface of InAs on Ga(1-x)In(x)Sb, but the abruptness of the interfaces would still be compatible. The RHEED intensity variations in the formation of the interfaces are discussed in terms of interface chemical reactions.

Fan, W. C.↗

NASA NTRS1991

Space vacuum processing

The unique ultra-vacuum environment of low-earth orbit space is to be utilized for vacuum processing of advanced semiconductor and superconductor materials through epitaxial thin-film growth. The quality of semiconductor single crystal (epitaxial) thin-films can be significantly enhanced in the space ultra-vacuum through the reduction of impurities. This will be accomplished by the development of the free-flying Wake Shield Facility presently being built by the Space Vacuum Epitaxy Center in conjunction with industry and NASA under a low-cost, short time commercial approach to space hardware development.

Ignatiev, A.↗

NASA NTRS1983

High-performance K-band GaAs power field-effect transistors prepared by molecular beam epitaxy

The maturity of the molecular beam epitaxy (MBE) technique for preparing device quality GaAs material for microwave applications is demonstrated by the excellent performance characteristics of K-band GaAs power field-effect transistors (FETs) fabricated on the MBE wafers. An output power of 710 mW with 4.5-dB gain and 17.7 percent power-added efficiency was achieved at 21 GHz with a 1.26-mm gate width pi-gate device. A similar device with a 0.56-mm gate width produced an output power of 320 mW with 5.0-dB gain and 26.6 percent power-added efficiency at 21 GHz. These are the best results yet reported to date for GaAs power FETs operated in the K-band frequency range.

Saunier, P.↗