On the energy distribution of interface states and their relaxation time profiles in Al/pentacene/p-GaAs heterojunction diode

Abstract

The energy density distribution profile of the interface states (Nss) and their relaxation time (τ) of Al/pentacene/p-GaAs heterojunction diodes were obtained from the admittance spectroscopy method, which is included in capacitance/conductance-voltage measurements in the frequency range of 10 kHz-1 MHz at room temperature. The values of Nss were also obtained from the forward bias current-voltage measurements by taking into account voltage-dependent barrier height, and the results were compared with those obtained using admittance method. The values of Nss and τ obtained from admittance measurements range from 1.53 × 1011 eV–1 cm–2 and 1.33 µs in (0.596-Ev) eV to 1.90 × 1011 eV–1 cm–2 and 8.18 µs in (0.673-Ev) eV, respectively. In addition, the values of Nss were obtained using Hill-Coleman method as a function of frequency. The values of Nss obtained from these three methods are in the same order and in good agreement with one another. Low values of Nss can be attributed to the interfacial pentacene layer between metal and semiconductor. This magnitude of Nss is very suitable for the fabrication of electronic devices. The C values of these diodes decrease with increasing frequency both in inversion and depletion regions, but give a peak in the accumulation region due to the effect of series resistance. The increase in C, especially at low frequencies, results from the presence of interface states at GaAs/pentacene interface.