Charge-based deep level transient spectroscopy of phosphorous-doped homoepitaxial diamond

Abstract

A form of charge-based deep level transient spectroscopy (Q-DLTS) has been used to investigate electrically active defects within three phosphorus (P)-doped, n-type, homoepitaxial diamond films, grown by the chemical vapor deposition technique, in an attempt to obtain a Q-DLTS signal related to the P-donor level itself. Four distinct peaks were observed in the Q-DLTS spectra, two of which could be fully analyzed. One of the other two peaks overlapped other structures in the measured spectra and so could not be fully characterized, while the fourth emerged at temperatures corresponding to the limit of the experimental system used. The two fully characterized peaks arose through the presence of levels with activation energies within the range 0.42–0.6 eV depending on the sample, contact scheme, and charging time used. One of these two peaks was only observed within two of the three samples. It occurred as a shoulder on the left-hand side of a more prominent and sharp Q-DLTS feature. Both of these Q-DLTS peaks are thought to originate from the P-related donor level in diamond, although their Q-DLTS activation energy values appeared to be scattered and most of the time significantly shallower than the value of 0.6 eV corresponding to the ground level of the P-related donor level. Such discrepancies are thought to arise essentially from retrapping effects, likely due to strong leakage currents at the metal/diamond interface. Improvements to the accuracy of the measurements made here is therefore expected if reliable, good quality, Schottky contacts to n-type diamond become obtainable.