Effect of low energy electron and UV irradiations on the charge condition of etched germanium surfaces

Abstract

Using field-effect and contact potential difference (c.p.d.) measurements the effect of low energy (180 to 960 V) electron irradiation on etched germanium surfaces has been studied. On all n- and p-type samples examined, a loss of negative charge was found to occur from the surface as shown by an increase in surface potential and decrease in c.p.d. with electron irradiation. Changes in c.p.d. were larger than changes in surface potential, the ratio being dependent on surface preparation. The difference between surface potential and c.p.d. changes can be explained by desorption of neutral atoms from the surface causing a change in surface dipole. UV irradiation above a threshold energy of approximately 5.0 eV was found to have a similar effect. If, however, dc fields were used for band-bending, it was found that changes in surface potential and c.p.d. were equal and hence as expected no desorption occurred.