Laser-assisted metalorganic chemical vapor deposition of zinc selenide
Shinn, Gregory B.
Doctor of Philosophy
Laser-assisted metalorganic chemical vapor deposition (LMOCVD) has been used to grow epitaxial zinc selenide at temperatures as low as 200$\sp\circ$C. The metalorganic sources, dimethylzinc (DMZ) and diethylselenide (DESe), were photodissociated with radiation from a 193 nm ArF excimer laser passing parallel to a (100) GaAs substrate. A two-stage purge scheme prevented deposition on the windows while minimizing disturbances to the gas flow in the growth region. The temperature dependence for both thermal and laser-assisted film growth was examined, keeping other reaction parameters fixed. The laser-assisted growth rate of ZnSe remained approximately constant at 1 $\mu$m/h over the temperature range 200-400$\sp\circ$C, temperatures at which no thermal growth occurs. At higher temperatures the thermally driven process was important and dominated the growth at temperatures above 500$\sp\circ$C. Photoluminescence analysis indicated that material grown at 400$\sp\circ$C by the laser-assisted process was of better quality than films grown by either method at other temperatures. The effects of laser energy density and repetition rate on growth rate were examined. The growth rate at 20 Hz increased from 1.1 $\mu$m/h at 15 mJ per pulse laser energy to 2.5 $\mu$m/h with a 48 mJ pulse energy with all other reactor conditions kept constant. Above a pulse energy of 40 mJ, the LMOCVD growth rates reached maximum values of about 2.7 $\mu$m/h and 4.6 $\mu$m/h for 20 Hz and 40 Hz operation, respectively. The rate was approximately doubled when the laser repetition rate was increased from 20 Hz to 40 Hz. A two-level design of experiments matrix was done to examine the effect of six reactor parameters on film growth rate. Increases in substrate temperature, dimethylzinc partial pressure, diethylselenide to dimethylzinc source ratio and use of the laser all resulted in higher growth rate while increased reactor pressure was found to decrease the film growth rate. A film grown with the laser radiation incident to the growth surface at a laser energy density of approximately 5 mJ/cm$\sp2$ exhibited the highest donor-bound exciton to self-activated center luminescence ratio of all films grown during this study.
Electronics; Electrical engineering