Narrow Results

A significant improvement of contact transfer resistance on undoped GaN/AlGaN/AlN (10 Å)/GaN high electron mobility transistor (HEMT) structure was demonstrated using a Ta/Ti/Al/Mo/Au metallization scheme compared to a Ti/Al/Mo/Au metallization scheme. A contact resistance as low as 0.16 ± 0.03 ohm-mm was achieved by rapid thermal annealing of evaporated Ta (125 Å)/Ti (150 Å)/Al (900 Å)/Mo(400 Å)/Au(500 Å) metal contact at 700 °C for 1 min followed by 800 °C for 30 sec in a N₂ ambient. An excellent edge acuity was also demonstrated for the annealed Ta/Ti/Al/Mo/Au ohmic contacts.

The formation of In_0.53Ga_0.47As/InP single quantum well with narrow well width grown by Organometallic Vapor Phase Epitaxy is verified by photoluminescence spectroscopy. PL spectra exhibit the e(1)-hh(1) transition in the well. PL measurement was conducted at various temperatures from 15 K to 200 K in order to investigate the important temperature-dependent parameters of this structure. Important parameters such as activation energies responsible for the photoluminescence quenching and broadening mechanisms are achieved. Because of small thermal activation energy of 15.1 meV in the narrow well, carriers can escape from the well to the barrier states. The dependence of PL width on temperature revealed that Inhomogeneous mechanism is the dominant mechanism for the broadening of PL peak and homogeneous mechanism is responsible at high temperature due to electron-phonon interaction.

Hot-electron fluctuation techniques were developed for experimental investigation of picosecond and subpicosecond electronic and phononic processes in voltage-biased 2DEG channels of interest for microwave low-noise and high-power transistors. Examples illustrate real-space transfer, hot-electron energy relaxation, and occupancy relaxation of hot-phonon modes. The pioneering results on hot-electron energy relaxation and hot-phonon lifetime are confirmed by time-resolved response experiments. The fluctuation technique for measuring the hot-phonon lifetime as a function of the hot-phonon temperature is unique, no datum has been reported for comparison as yet.