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AlGaAs/GaAs double‐heterojunction high electron mobility transistors (DHHEMTs) grown by low‐pressure organometallic vapor phase epitaxy are reported in this communication. The magnetic field‐dependent Hall effect measurement was used to characterize the sheet carrier density and electron mobility of the two‐dimensional electron gas (2‐DEG). At 77 K the sheet carrier density and the electron mobility were 1.38×1012 cm−2 and 52 900 cm2 /V s, respectively, in a DHHEMT structure with an undoped Al0.28Ga0.72As spacer layer of 120 A, while they were 7.12×1011 cm−2 and 65 100 cm2 /V s, respectively, in a comparable single‐heterojunction HEMT structure. DHHEMT’s with 0.5‐μm‐gate length and 75‐μm‐gate width have been fabricated with dc saturation current of 500 mA/mm and dc transconductance of 250 mS/mm. These results are comparable to those produced with molecular‐beam epitaxy.

In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (one-dimensional finite element systems). The objective of this dissertation research is to extend TSV and SVM from one-dimensional finite element systems to multi-dimensional ones and from statics to vibration and sensitivity analysis. Meanwhile, four new interesting and useful properties of finite element systems are also revealed. One of them is stated as the Gradient Orthogonality Theorem of Basic Displacements, based upon which a set of explicit formulations are derived for design sensitivities of displacements, internal forces, stresses and even the inverse of the global stiffness matrix of a statically loaded structure. The other three new properties are described as the Evaluation Theorem of Principal Z-Deformations, the Monotonousness Theorem of Principal Z-Deformations and the Equivalence Theorem of Basic Displacement Vectors and Eigenvectors, based upon which a new approach, called the Z-deformation method, is developed for vibration analysis of finite element systems. This method is superior to the commonly used inverse power iteration method when adjacent eigenvalues are close. Explicit formulations for eigenpair sensitivities are also derived in accordance with the Z-deformation method. The distinct feature of TSV and SVM is that the analysis results for a loaded structure can be obtained without any matrix assembling and inverse operations. This feature gives TSV and SVM an edge over the traditional finite element analysis in many engineering applications, where the repeated analysis is required, such as structural optimization, reliability analysis, elastic-plastic analysis, vibration, contact problems, crack propagation in solids.

The bit error ratio (BER) performance of a 1.2-Gbit/s lightwave transmission system using 1.3-μm InGaAsP Fabry-Perot (FP) laser diodes with Zn-doped active layers was investigated experimentally. When the laser diodes were tested through a dispersive: fiber, turn-on jitter and mode-partitioning of the lasers contributed to pulse jitter of the optical waveform at the receiver, which in turn led to a dispersion power penalty. It was found that the pulse jitter and the resulting power penalty were strongly dependent on the carrier lifetime of the lasers. Since the doping level of the active layer affects the carrier lifetime, this suggests that doped-active FP laser diodes with a decreased carrier lifetime may be usable in a wider range of gigabit lightwave applications than previously considered.

The fabrication and performance of high-speed and low relative intensity noise (RIN) 1.3 micrometers InGaAsP semi-insulating buried crescent (SIBC) Fabry-Perot (FP) lasers with Zn- doped active layers are reported. These SIBC lasers have a 3-dB modulation bandwidth of 19 GHz for pulsed operation and 16 GHz for cw operation, and a RIN below -150 dB/Hz for biased current at 120 mA. This is the highest modulation bandwidth yet reported for InGaAsP lasers with semi-insulating current blocking layers.

The novel concept of K-stabilizing layer is reported for the first time. The coupling coefficient (K) which determines the characteristics of distributed feedback laser diodes (DFB LDs) has been controlled by optimizing the grating depth and layer thicknesses. The coupling coefficient is less dependent on the variations of grating depth and layer thicknesses if an optimized K- stabilizing layer (lower index material like InP) is inserted between the active layer and the guide layer. The controllability of the coupling coefficient has been demonstrated by the standard deviation of the lasing wavelength and the threshold current across a wafer, 0.74 nm and 2.67 mA, respectively.

We have investigated, experimentally, the coherent operation of 1-dimensional linear arrays of grating coupled surface emitting lasers for different laser designs (gain lengths, grating parameters). For laser arrays with shailow grating teeth and strong inter-element coupling a diffraction limited far field of 0.012 degrees full width half maximum was obtained from up to 6 coupled lasers extending over a length of 3.5mm.