Chien-Ping Lee

Carrier injection and backgating effect in GaAs MESFET's

The relation between the backgating effects on GaAs MESFETs and current conduction in the semi-insulating substrate is studied. The onset voltage of the backgating effect is found to coincide with the trap-fill-limited voltage for the substrate conduction. This observation implies that carrier injection in the substrate is directly related to the backgating effect.

Computer simulation of electron energy levels for different shape InAs/GaAs semiconductor quantum dots

Abstract A computational technique for the energy levels calculation of an electron confined by a 3D InAs quantum dot (QD) embedded in GaAs semiconductor matrix is presented. Based on the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, a finite height hard-wall 3D confinement potential, and the Ben Daniel–Duke boundary conditions, the problem is formulated and solved for the disk, ellipsoid, and conical-shaped InAs/GaAs QDs. To calculate the ground state and first excited state energy levels, the nonlinear 3D Schrodinger is solved with a developed nonlinear iterative algorithm to obtain the final self-consistent solutions. In the iteration loops, the Schrodinger equation is discretized with a nonuniform mesh finite difference method, and the corresponding matrix eigenvalue problem is solved with the balanced and shifted QR method. The proposed computational method has a monotonically convergent property for all simulation cases. The computed results show that for different quantum dot shapes, the parabolic band approximation is applicable only for relatively large dot volume. For the first excited states the non-parabolicity effect also has been found to be stronger than it at ground state. The QD model and numerical method presented here provide a novel way to calculate the energy levels of QD and it is also useful to clarify principal dependencies of QD energy states on material band parameter and QDs size for various QD shapes.

Integration of an injection laser with a Gunn oscillator on a semi‐insulating GaAs substrate

The integration of an injection semiconductor laser with an active electronic device (Gunn oscillator) in a single epitaxial crystal device is demonstrated.

Direct transmission of pictorial information in multimode optical fibers

The problem of coherent image transmission through a single multimode optical fiber is discussed. A scheme is presented for recovering the transmitted image after distortions brought about by the fiber modes dispersion. Realization of this scheme by holographic techniques and with lens systems is proposed, and its limitations pointed out. The application of this scheme in canceling out temporal signal dispersion in a multimode fiber transmission line is also discussed briefly.

Mechanism of surface conduction in semi‐insulating GaAs

The space‐charge‐limited current leakage in processed semi‐insulating GaAs wafer has been found to occur very close to the surface. The depth profile of the EL2 traps has been calculated from the measured trap‐fill‐limited voltage (Vt) of the leakage current versus etch depth and agrees well with the reported experimental result. A proposed mechanism of surface conduction is presented based on EL2 outdiffusion. The calculated substrate I‐V relation agrees quantitatively with the measured results.

Q‐switched ruby laser alloying of Ohmic contacts on gallium arsenide epilayers

Ohmic contacts of AuGe have been produced on GaAs epilayers by laser alloying. The contacts possess morphological and electrical properties which are superior to those formed by conventional alloying.

Time-domain and spectral-domain investigation of inflection-point slow-light modes in photonic crystal coupled waveguides.

We report on spectral-domain and time-domain measurements and numerical calculations of group velocities in a photonic crystal coupled waveguide, where the unique guided mode band structure has a flat band region within the photonic band gap allowing for slow light observation. The spectral dependence of group velocity, which is measured by interference method, indicates the existence of slow light modes around the inflection point of the unique flat band, rather than at the band edge. Time-domain observation of optical pulses propagating along two-dimension slab photonic crystal coupled waveguides is also demonstrated by using a high speed oscilloscope. By adjusting the wavelength of the input pulses toward the flat band of the coupled defect modes, an increasing duration time between reference and output pulses are clearly observed. An extremely small group velocity of 0.017c is thus obtained. Calculated group velocities show good agreement with our measured results.

The Safe Operating Area of GaAs-Based Heterojunction Bipolar Transistors

The safe operating area (SOA) of GaAs-based heterojunction bipolar transistors has been studied considering both the self-heating effect and the breakdown effect. The Kirk effect induced breakdown (KIB) was considered to account for the decrease of the breakdown voltage at high currents. With reasonable emitter ballastors, the KIB effect was shown to be the major cause for device failure at high currents, while the thermal effect controls the low current failure. The effect of emitter resistance and base resistance on device stability was also studied. While the emitter resistance always improves the device stability by expanding the SOAs, the base resistance degrades SOAs when the KIB dominates the failure mechanism. The effect of the base resistance on SOAs was explained by its control on the flow of the avalanche current. Since the KIB effect depends on the collector structure, it was shown that a nonuniformly doped collector can effectively improve the SOAs

GaAs‐GaAlAs injection lasers on semi‐insulating substrates using laterally diffused junctions

Low‐threshold GaAs‐GaAlAs lasers operating in a stable single mode have been fabricated using laterally diffused junctions. The lasers are fabricated on semi‐insulating substrates and can be integrated with other components.

Electron energy level calculations for cylindrical narrow gap semiconductor quantum dot

Three computational techniques are presented for approximation of the ground state energy and wave function of an electron confined by a disk-shaped InAs quantum dot (QD) embedded in GaAs matrix. The problem is treated with the effective one electronic band Hamiltonian, the energy and position dependent electron effective mass approximation, and the Ben-Daniel Duke boundary conditions. To solve the three dimensional (3D) Schrodinger equation, we employ (i) the adiabatic approximation, (ii) the adiabatic approximation with averaging, and (iii) full numerical solution. It is shown that the more efficient approximations (i) and (ii) can only be used for relatively large QD sizes. The full numerical method gives qualitative as well as quantitative trends in electronic properties with various parameters.