**Thesis Type:** Doctorate

**Institution Of The Thesis:** Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

**Approval Date:** 2017

**Student:** SEÇKİN ALTINDAL YERİŞKİN

**Supervisor: **MUZAFFER BALBAŞI

In this study, Au/Au/%7 graphene-doped PVA/n-Si (MPS) structure were prepared and their posible current-conduction mechanisms have been investigated based on Thermionic emisiyon (TE) in the temperature range of 80-380 K by using the forward bias current-voltage (I-V) measurements. Experimental results show that the values of zero-bias barrier height (Bo) increase with increasing temperature contarary to literature, whereas ideality factor (n) decreases. Φap vs q/2kT plot was drawn to obtain an evidence of a Gaussian distribution (GD) of the barrier heights (BHs) and it revealed two distinct linear regions with different slopes and intercepts. The mean values of BH ( and zero-bias standard deviation (σso) were obtained from the intercept and slope of these linear plots as 1.30 eV and 0.16 V for the first region (280-380 K) and 0.74 eV and 0.085 V for the second region (80-240 K), respectively. Thus, the values ofBo and effective Richardson constant (A*) were also found from the intercept and slope of the modified Richardson plot (ln(Is/T2)-q2o2/2k2T2 vs q/kT) for two linear regions as 1.31 eV and 130 A/cm2 K2 for the first region and 0.76 eV and 922 A/cm2 K2 for the second region, respectively. This value of A* for the first region is very close to the theoretical value of 112 A/cm2K2 for n-Si. Thus the forward bias I-V characteristics of the structure can be successfully explained on the basis of TE mechanism with double (DGD) of BHs.The energy density distribution profile of surface states (Nss) was also extracted from the forward bias I-V data by taking into account voltage dependent effective BH (e) and n. In addition, dielectric properties, eelctric modulus and electrical conductivity of these structures were obtained from the capacitance-voltage (C-V) and conductance-voltage (G/-V) measurements in the frequency range of 0.5 kHz - 1 MHz at room temperature. The changes in these parameters become more high at low frequencies due to interfacial and dipole polarizations and Nss. The vs log(f) plot exhibited both low and high frequency dispersion phenomena such that at low frequencies value corresponding to the dc conductivity (dc), but at high frequencies it corresponds to the ac conductivity (ac).