--------------------------------------------------------------------
       SEMINAR OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
        Institute for Computational Sciences and Informatics
  CSI 929  (http://science.gmu.edu/physics/seminar/schedule.html)
--------------------------------------------------------------------
		Ion-implantation doping of SiC and GaN

			Mulpuri V. Rao
	Deptment of Electrical and Computer Engineering
	           George Mason University

Ion implantation is the only selective area doping technique available 
for the fabrication of palanar SiC and GaN integrated circuits. Thermal 
diffusion is not feasible due to the low diffusion coefficient of the 
dopants at temperatures where thermal dissociation of the compound 
does not occur. We have performed N and Al ion implantations into 
6H-SiC at elevated temperatures (700-800 C) to obtain n- and p-type 
regions, respectively. Post-implantation annealing was performed 
using a ceramic processing furnace or microwaves. The annealings 
were performed at temperatures up to 1600 C. The N implantation 
yielded n-type regions with a maximum room temperature carrier 
concentration of 2 10^19 cm-3 and good crystalline quality. Diodes 
made by N implantation into p-type 6H-SiC have a forward turn-on 
voltage of 2.2 V and an ideality factor of 1.9 with nA range reverse 
leakage current. The Al implantation gave p-type regions with high 
10^18 cm-3 range room temperature carrier concentration.
Since annealing is a required step after implantation, heat 
treatment studies wre performed on GaN layers grown on sapphire. 
For rapid thermal annealing (RTA), formation of liquid Ga droplets, 
due to N evaporation, is observed on the GaN surface after 1100 C 
annealing. Evaporation of N can be minimized by using a GaN or SI3N4 
proximity cap during annealing. Activation of the Si implant was 
observed only for annealing temperatures > 1100 C. Higher Si 
activation was observed when the implants were perfomed at elevated 
temperatures. No activation of Mg was observed with or without P 
coimplantation.

                          Monday , April 22 1996
                                  5:00 pm
                          Room 206, Science & Tech. I
-------------------------------------------------------------------