The search for donors in diamond

One of the major issues in diamond electronics is the search for a useful n -type dopant. Nitrogen is a well-known, yet very deep, donor in diamond. Ph osphor has been shown to have a rather deep donor level in diamond (E-a sim ilar to 0.5 eV) and the electron mobility values achieved so far for CVD-gr own P-containing diamond layers are still rather low. Interstitial Li, whic h has been predicted to act as a donor in diamond, has, so far, not yielded any convincing, useful electron conductivities. Sulfur has recently been r eported to have a donor level in diamond; however, these results need furth er checks, due to some B contamination found in the S-doped samples. Attemp ts to dope diamond with P and with S by ion implantation have not yet yield ed any significant donor signature. On the other hand, point defect-related electrical conductivity in diamond (as induced by ion or electron irradiat ion) was shown to act as compensating donors to B-doped diamond, and has be en proven to yield rectifying junctions with p-type diamond. Ab initio comp uter simulations for diamond containing different dopant impurities show th at substitutional S in diamond should have a rather shallow donor level (0. 2 eV), with a formation energy lower then that of P. Hence sulfur could act as a useful shallow donor in diamond. This prediction has, however, not be en experimentally confirmed as yet. In the present work we will review the experimental and theoretical status of n-type diamond, as well speculate on other possible donor states in diamond. (C) 2001 Elsevier Science B.V. All rights reserved.