In this thesis, we successfully fabricated patterned semiconductor substrates, edge-emitting lasers with deeply etched distributed Bragg reflectors (DBRs), two-dimensional photonic crystals (2DPCs) and two-dimensional photonic crystal microcavities (2DPC microcavities) by electron-beam lithography and inductively coupled plasma-reactive ion etching (ICP-RIE). We have obtained a minimum writing linewidth of 50nm and a maximum writing range of 500¡Ñ500µm2 in our electron-beam lithography system. Pitch arrays of 100nm pitch-diameter and 100nm separation have been formed on 100¡Ñ100µm2 semiconductor substrates. The etching depth of patterned Si substrates and patterned GaAs substrates are 50nm and 20nm, respectively. In the design of edge-emitting lasers with deeply etched DBRs, two and three pairs of DBRs were formed on the edge of laser cavity, respectively. To obtain high reflectance at wavelength (£f) = 960nm, 209nm mirror width and 240nm or 720nm air gap were fabricated. In the design of 2DPCs, a triangular array of air columns was adopted. The lattice constant (A) and column radius (R) are 742nm and 327nm, respectively. It has a band gap for TE modes corresponding to wavelength range in 936.45nm~968.85nm. We placed single defect in the 2DPCs to form 2DPC microcavities. In addition, we simulated the photonic band structure of a seven-defect 2DPC microcavity with A = 224nm and R = 56nm. We obtained a monopole defect mode at £f = 959.86nm. To measure 2DPCs and 2DPC microcavities, we have set up a micro-photoluminescence (Micro-PL) spectrum measurement system. We observed the Micro-PL intensity of the 2DPC microcavity is 4.5 times larger than 2DPCs at £f = 960nm in the same pumping power. The 2DPC microcavities show a lasing performance under optical pumping. The threshold power of 2DPC microcavities is 5.13mW~6.81mW at room temperature and decreases to 1.4mW~3.13mW at 15¢J.

AlGaN/GaN high electron mobility transistors (HEMTs) have been widely used for high power and high frequency RF communications due to their fast switching and large current handling capabilities. The reliability of such devices is strongly affected by the junction temperature where the highest magnitude occurs in a local region on the drain side edge of the gate called the hotspot. Thus, thermal management of these devices remains a major concern in the design and reliability of systems employing AlGaN/GaN HEMTs. Due to the large power densities induced in these devices locally near the drain side edge of the gate, it is clear that moving thermal management solutions closer to the heat generation region is critical in order to reduce the overall junction temperature of the device. In this work, we explore the use of embedded microchannel cooling in the substrate of AlGaN/GaN HEMTs made on Si and SiC substrates and compare them to passive cooling techniques using Si, SiC, and diamond substrates. In addition, the impact of cooling fluids and harsh environmental conditions were considered. The study was performed using a combination of CFD and finite volume analysis on packaged AlGaN/GaN HEMTs. Active cooling using embedded microchannels were shown to have a significant impact on the heat dissipation over the passive cooling methods, approaching or exceeding that of diamond cooled devices. For vertical power devices (IGBT), embedded microchannels in the power electronics substrates were explored. In both the power devices and lateral AlGaN/GaN HEMTs, the use of embedded microchannels with nonlinear channel geometries was shown to be the most effective in terms of reducing the device junction temperature while minimizing the pumping power required.