Transient photovoltage in GaN

Abstract

We studied restoration of the band bending at the surface of undoped GaN layers after illumination with pulses of the above-bandgap light. The absolute value of band bending and transients of the photovoltage were measured with an atomic force microscope in the surface potential mode (Kelvin probe method). The photovoltage transients following very weak excitation with a single pulse of light could be well fitted within a simple phenomenological model accounting for charging of the acceptor-like surface states by free electrons after the light pulse. Photo-induced desorption of ions at the surface and recharging of a surface oxide layer may also affect the value and transients of the photovoltage, particularly if the illumination is prolonged.

Thermal stability of DRL in n‐GaN

“…3 Results Figure 1 shows normalized to the maximum value CL spectra of a-screw dislocation rich (solid lines) and dislocation free regions (dot lines) at 70 and 300 K. CL spectrum of dislocation free region at 70 K consist of the band of free exciton (FE) at 3.47 eV, and two low intense bands at 3.27 and 3.4 eV that were previously ascribed to the recombination of donor-acceptor pairs or to second phonon replica of FE and exciton bound at point defects, respectively [11]. The main CL-feature of a-screw dislocations was DRL band at energies of about 3.18 eV at 70 K and 3.12 eV at 300 K, the intensity of which exceeded well the intensity of FE (see Fig.…”

Effect of ambient on electrical and optical properties of GaN

“…(2) and a more detailed discussion of SPV transients will be reported elsewhere. 17 The SPV decay strongly depended on both the ambient and the illumination time. After a short UV exposure (up to 5 s), the SPV decay behavior in vacuum and air ambient were similar (Fig.…”

“…Previously, we estimated the absolute value of band bending in dark, 0 Φ , from Kelvin probe measurements. 3,8 The band bending can be calculated for these Kelvin probe studies using the following relationship: 3,6 0 ( )…”

“…7 In addition, an analysis of photovoltage transients after pulsed illumination with various light intensities can distinguish contributions between intrinsic surface states and electronic states induced by adsorbed ions. 8 In recent years, scanning Kelvin probe microscopy (SKPM) at room temperature and air ambient has been successfully employed for the surface potential mapping of GaN. These measurements are typically correlated with atomic force microscopy (AFM) images and provide information about local changes of band bending due to the presence of charged defects, e.g.…”