Injection dependent long carrier lifetimes in high quality CVD diamond

In this paper we report an experimental study of photocurrent mobility x li fetime products and free carrier lifetimes in CVD grown polycrystalline dia mond of various qualities. The investigated samples are low impurity sample s, nitrogen content similar to 10(15) cm(-3), with an average grain size ra nging from 25 mum up to 110 mum. This large difference in average grain siz e makes it possible to distinguish effects due to Lifetime limiting trappin g and recombination defect centers inside the grains from effects caused by defect centers at grain boundaries. At low carrier densities, < 10(13) cm( -3) the effective free carrier lifetime is in the sub-nanosecond to nanosec ond range in all samples due to intra-grain trapping and recombination cent ers. At high carrier densities, > 10(13) cm(-3), the intra-grain centers be comes saturated and the effective lifetime becomes predominately given by c arrier diffusion to and recombination at the defects related to the grain b oundaries. Hence, the effective lifetime at high carrier densities is stron gly related to the average grain size and increases up to several tens of n anoseconds, in samples with a large average grain size, whereas it remains in the nanosecond range for samples with small average grain size. In addit ion, we observe a lower mobility x lifetime product and decay constant with increasing nitrogen content, clearly showing the negative influence of nit rogen and nitrogen-related defects on these important material parameters. (C) 2001 Elsevier Science B.V. All rights reserved.