Surface Photovoltage Spectroscopy of Ultrawide Bandgap Materials

Techniques of surface photovoltage (SPV) spectroscopy allow for the highly sensitive characterization of transitions in ultrawide bandgap materials without the need for contact preparation. Furthermore, SPV techniques can give access to electronic transitions at buried interfaces. Tools for continuous measurements of dc, ac (modulated), and ac (transient) SPV signals with the same perforated electrode and a charge amplifier are developed for spectral ranges from the near infrared up to the deep ultraviolet and for time domains from the ns to s…h to ranges. The analysis of modulated SPV transients is applied. The high empirical potential of SPV spectroscopy is demonstrated by studies of a diamond single crystal, a layer of β‐Ga 2 O 3 grown by pulsed laser deposition, and an AlN layer epitaxially grown on sapphire. Defect‐related transitions are characterized over the entire bandgap for all mentioned materials. Several phonon‐assisted transitions near the bandgap of diamond are well detected. Different defect transitions dominating near the β‐Ga 2 O 3 surface or near the β‐Ga 2 O 3 /sapphire interface are distinguished. Several defect transitions near the bandgap of AlN are observed. Uncertainties for interpretation of transition energies are discussed.