Charge carrier trapping by dislocations in single crystal diamond

Charge carrier trapping in diamond crystals containing well-defined concentrations of dislocations was investigated by several complementary techniques. Samples with dislocation densities n(dis) between <1x10(7) and approximate to 1x10(9)cm(-2) were grown heteroepitaxially on Ir/YSZ/Si(001). In optical pump-probe experiments, ambipolar diffusion coefficients were determined from the decay of light-induced transient free carrier gratings. Modeling their variation with excitation density yielded trapping cross sections sigma of 29 and 10nm for the dislocations and a stress-field-induced reduction in exciton binding energies from 80 to 73 and 60meV at n(dis)=1x10(8) and 1x10(9)cm(-2), respectively. The lifetime measured by induced absorption scaled proportional to 1/n(dis) with absolute values ranging from 0.1 to 10ns. In the electrical measurements on two sets of detector slices, electron-hole pairs were excited by alpha-particles and transport was measured separately for electrons and holes. Both types of carriers showed fast transient current signals. The time constant of the additional slow component exclusively seen for holes was in agreement with the activation energy of boron acceptors. Their concentration of approximate to 0.5ppb yielded sigma=1.77x10(-13)cm(2) for charged point traps. Schubweg and carrier lifetime due to deep trapping roughly reproduced the 1/n(dis) trend. For electrons at 3V/mu m, a value sigma=40nm was deduced. Cross sections for holes were significantly smaller. Differences in hole trapping between the samples are attributed to charging of dislocations controlled by chemical impurities. Increase in lifetime at high voltages is explained by reduced capture cross sections for hot carriers.