Characterizing of Zinc Oxide (ZnO) as a Transparent Conducting Oxide (TCO). ANDREA VERMEER (Seattle Pacific University Seattle, WA 98119) XIAONAN LI (National Renewable Energy Laboratory, Golden, CO, 89401)

The purpose of this investigation was to characterize undoped insulating zinc oxide (i-ZnO) as a transparent conducting oxide (TCO). We studied the optical, electrical, and structural properties of the metal oxide as it was deposited by two different methods: MOCVD (metal-organic chemical vapor deposition) and PECVD (plasma enhanced chemical vapor deposition). The films were etched using plater's tape or black wax and hydrochloric acid. The thickness of each film was measured using a Dektak3 stylus profilometer. Transmission, reflection, and absorption spectrums were analyzed between 300 nm to 2000 nm using a Cary spectrophotometer. Through use of the Bio-Rad HL5500 Hall system, the carrier concentration, resistivity, and mobility of each film were measured. A Scintag X-ray Diffraction machine (XRD) was used to determine the lattice constants and presence of crystalline structures within the thin films. Three sample sets were studied: a set of undoped ZnO films was deposited by MOCVD at temperatures ranging from 200 C to 550 C as well as two sets of undoped ZnO films deposited by PECVD, one set ranging from room temperature to 400 C at a fixed power of 50 watts and one set ranging from 25 watts to 150 watts at a fixed temperature of 200 C. With increased deposition temperatures in MOCVD, the films demonstrated strong preferred (0 0 2) orientation. As the temperature increased, the samples deposited by MOCVD had increased resistivity and decreased carrier concentration. The films deposited by PECVD tended to have a stronger preferred orientation (0 0 2) as the power decreased and the temperature increased. The resistivity of the films deposited by the PECVD decreased with temperature and the carrier concentration increased. The resistivity of the films deposited by the PECVD increased with power at first, then decreased and the carrier concentration increased with increased power. Most of the samples demonstrated transmission that was greater than eighty percent and lattice constants tended to be above the standard. From this data we were able to determine the optimal MOCVD and PECVD deposition conditions for i-ZnO.

Dislocation Generation Under Controlled Thermal Stress. DOUGLAS GAGNON (Cornell University Ithaca, NY 14850) BHUSHAN SOPORI (National Renewable Energy Laboratory, Golden, CO, 89401)

The objective of this project was to produce dislocations of desired density and with a nearly-uniform distribution in silicon wafers. The dislocations were generated by applying thermal stress to silicon wafers via an optical processing furnace. Controlled stresses were produced by different spatial distributions of temperature. The temperature of the wafers was measured using Chromel/Alumel thermocouples attached to the underside. The temperature of each thermocouple, as well as its spatial location on the wafer, was recorded by a computed program, which graphed the temperature recorded over time. The samples were then defect etched and their dislocations maps were generated by PVSCAN, an instrument that rapidly produces maps of surface defects.

Testing For Linearity Using A Two Lamp Method. DEREK NALLEY (Purdue University West Lafayette, IN 47907) KEITH A. EMERY (National Renewable Energy Laboratory, Golden, CO, 89401)

Photovoltaic devices are rated in terms of their power output or efficiency with respect to a specific spectrum, total irradiance, and temperature. In order to rate photovoltaic devices a reference detector whose response is linear with total irradiance is needed. This procedure documents a procedure to determine if a detector is linear over the irradiance range of interest. Testing the short circuit current versus the total irradiance is done by illuminating a reference cell candidate with two lamps that are fitted with programmable filter wheels. The purpose is to reject nonlinear samples as determined by national and international standards from being used as primary reference cells. A calibrated linear reference cell tested by the two lamp method yields a linear result.