Electrical properties of undoped and ion-implanted type IIa diamonds measured by photo-Hall

Abstract

The reasons why no reliable n-type chemical doping can be obtained in P implanted and annealed diamond is addressed by studying the nature and conductivity type of the compensating defects and their interactions with both n- and p-type implanted dopants using optical (absorption and photoluminescence) and low temperature (20< T<300 K) photo-Hall and measurements. Type IIa natural diamond samples are implanted with C, B and P to doses and energies such that identical defect concentration profiles are achieved for all three ions. Measurements are carried out on the virgin (IIa) diamond, on the as-implanted and implanted and annealed (1300 C, 20 min) diamond layers. We show that the photo-excited carriers are always holes with rather high mobilities. The acceptor level in undamaged type IIa diamond is located at mid-gap (above 2.3 eV). Ion implantation leads to an increase in hole concentration by about 2 orders of magnitude, with still remarkable high mobilities. The electrical properties of the implanted samples are analyzed by considering that some of the carriers photo-generated in the implanted layer diffuse into the undamaged part of the sample in which they assume the measured very high mobility. A two layer model is used to analyze the data in conjunction with solving the continuity equations in both implantation affected layer (∼0.5 μm) and the unaffected substrate yielding substantially lower mobilities (10–100 cm 2/V s) for the implanted layer alone.