Electric field gradient dependence of excess avalanche noise

Electron initiated avalanche noise measurements were performed on two Al/sub 0.3/Ga/sub 0.7/As pn/sup +/ diodes with p-region doping density N/sub a/=1.6/spl times/10/sup 17/ cm/sup -3/ and N/sub a/=5.0/spl times/10/sup 17/ cm/sup -3/ and two Al/sub 0.3/Ga/sub 0.7/As p/sup +/n structures with n-region doping density N/sub d/=1.0/spl times/10/sup 17/ cm/sup -3/ and N/sub d/=4.6/spl times/10/sup 17/ cm/sup -3/. The avalanche noise was found to decrease with increasing doping concentration in all structures and was found to be lower in the p/sup +/n structures than in the pn/sup +/ structures. The results are interpreted in terms of spatial coherence of the ionisation process.