Yasemin Şafak

Electrical characterization of MS and MIS structures on AlGaN/AlN/GaN heterostructures

The forward and reverse bias I–V, C–V, and G/x–V characteristics of (Ni/Au) Schottky barrier diodes (SBDs) on the Al0.22Ga0.78N/AlN/GaN high-electron-mobility-transistor (HEMTs) without and with SiNx insulator layer were measured at room temperature in order to investigate the effects of the insulator layer (SiNx) on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (UB0), series resistance (Rs), interface-state density (Nss). The energy density distribution profiles of the Nss were obtained from the forward bias I–V characteristics by taking into account the voltage dependence of the effective barrier height (Ue) and ideality factor (nV) of devices. In addition, the Nss as a function of Ec–Ess was determined from the low-high frequency capacitance methods. It was found that the values of Nss and Rs in SBD HEMTs decreases with increasing insulator layer thickness.

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

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 lay...