The influence of excited states of deep dopants on majority-carrier concentration in a wide-bandgap semiconductor

The influence of the excited states of a substitutional dopant (donor or acceptor) on the majority-carrier concentration in a wide-bandgap semiconductor is investigated theoretically and experimentally, because acceptor levels DeltaE(A) in SiC, GaN and diamond were reported to be deeper than 150 meV. In order to accurately determine the values of DeltaE(A), the acceptor density N-A and the compensating density N-comp in Al-doped p-type 4H-SiC using the temperature dependence p ( T) of the hole concentration obtained from Hall-effect measurements, a distribution function including this influence is theoretically derived. Here, an ensemble average (E-ex) over bar of the ground and excited state levels of the acceptor is newly introduced into the distribution function. It is found that a curve-fitting procedure, in which we proceed to search for N-A, DeltaE(A) and N-comp to fit a curve to the experimental p (T) by a method of least squares, is not suitable for investigating this influence. It is experimentally demonstrated that free-carrier concentration spectroscopy (FCCS), which we have proposed, can investigate this influence in detail. By using FCCS and the distribution function proposed here, the reliable values of N-A, DeltaE(A) and N-comp can be obtained.