V. Janardhanam

Conduction Mechanism of Se Schottky Contact to n-Type Ge

The conduction mechanism of Se/n-type-Ge Schottky diodes is investigated using temperature-dependent current-voltage (I- V) characteristics. The presence of microscopic inhomogeneity at the Se/Ge interface could be the primary cause of the differences between the barrier heights measured from the I-V and capacitance-voltage (C-V ) characteristics. The position of the quasi-Fermi level suggested the dominance of thermionic emission in the forward bias region. The electric field dependence of the reverse current revealed that Schottky emission, along with the generation mechanism, has dominance over the current conduction in the reverse bias region.

Electrical properties of Au/Bi0.5Na0.5TiO3-BaTiO3/n-GaN metal?insulator?semiconductor (MIS) structure

We investigated the electrical properties of solution processed high-k Bi0.5Na0.5TiO3(BNT)-BaTiO3(BT) on n-GaN with Au electrode. Higher barrier height is obtained for Au/BNT-BT/n-GaN structure compared to Au/n-GaN structure. Thin interfacial layer is formed in between BNT-BT and n-GaN confirmed by TEM results. The interface state density of Au/BNT-BT/n-GaN structure is lower than that of Au/n-GaN structure due to the existence of interfacial layer (Ga-O) at the interface. It is observed that the frequency dispersion is decreased in the Au/BNT-BT/n-GaN structure. Poole?Frenkel mechanism is found to dominate the reverse leakage current in both Au/n-GaN and Au/BNT-BT/n-GaN structures.

Microstructural, electrical and frequency-dependent properties of Au/p-Cu2ZnSnS4/n-GaN heterojunction

An Au/Cu2ZnSnS4 (CZTS)/n-GaN heterojunction (HJ) is fabricated with a CZTS interlayer and probed its chemical states, structural, electrical and frequency-dependent characteristics by XPS, TEM, I-V and C-V measurements. XPS and TEM results confirmed that the CZTS films are formed on the n-GaN surface. The band gap of deposited CZTS film is found to be 1.55eV. The electrical properties of HJ correlated with the Au/n-GaN Schottky junction (SJ). The Au/CZTS/n-GaN HJ reveals a good rectification nature with high barrier height (0.82eV) compared to the Au/n-GaN SJ (0.69eV), which suggests the barrier height is influenced by the CZTS interlayer. The barrier height values assessed by I-V, Cheungs and Norde functions are closely matched with one other, thus the methods used here are reliable and valid. The extracted interface state density (NSS) of Au/CZTS/n-GaN HJ is lower compared to the Au/n-GaN SJ that suggests the CZTS interlayer plays an important role in the reduction of NSS. Moreover, the capacitance-frequency (C-f) and conductance-frequency (G-f) characteristics of SJ and HJ are measured in the range of 1kHz-1MHz, and found that the capacitance and conductance strappingly dependent on frequency. It is found that the NSS estimated from C-f and G-f characteristics is lower compared to those estimated from I-V characteristics. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current in both SJ and HJ, probably related to the structural defects and trap levels in the CZTS interlayer.

Rapid thermal annealing effects on the electrical, structural and morphological properties of Yb/ p -type InP Schottky Structure

The electrical, structural and surface morphological properties of Yb/p-InP Schottky barrier diode (SBD) have been investigated at different annealing temperatures. The determined Schottky barrier height (SBH) and ideality factor n of the as-deposited Yb/p-InP SBD are 0.68 eV (I-V)/0.81 eV((C-V)) and 1.44 respectively. After annealing at 300℃, the SBH of Yb/p-InP SBD increases to 0.72 eV (I-V)/0.88 eV ((C-V)). When the contact is annealed at 400℃, the SBH slightly decreases to 0.67 eV (I-V)/0.80 eV ((C-V)). These results reveal that the optimum annealing temperature for Yb/p-InP SBD is 300℃. Cheung’s functions are also employed to determine the series resistance of the Yb/p-InP SBD. Using Terman’s method, the interface state density is estimated for Yb/p-InP SBD at different annealing temperatures. The XPS results reveal that the existence of phosphorous-rich surface after the annealing. The AES and XRD results showed that the formation of phosphide phases at the Yb/p-InP interface may be the reason for the increase of SBH after annealing at 300℃. The decrease in the BH after annealing at 400℃ may be due to the formation of indium phases at the interface. The overall surface morphology of the Yb Schottky contact is fairly smooth at elevated temperatures.

Electrical and Microstructural Properties of Pt-Germanides Formed on p-Type Ge Substrate

Formed on p-Type Ge Substrate V. Janardhanam, Jin-Sung Kim, Kyungwon Moon, Young-Boo Lee, Do-Geun Kim, Seung-Min Kang, and Chel-Jong Choi Department of BIN Fusion Technology, Chonbuk National University, Jeonju 561-756, Korea Jeonju Center, Korea Basic Science Institute, Jeonju 561-756, Korea Materials Processing Division, Korea Institute of Materials Science, Changwon 640-010, Korea Department of Advanced Materials Science and Engineering, Hanseo University, Seosan 360-706, Korea School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, Korea

Modification of Schottky Barrier Properties of Ti/p-type InP Schottky Diode by Polyaniline (PANI) Organic Interlayer

The electrical properties of Ti/p-type InP Schottky diodes with and without polyaniline (PANI) interlayer was investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. The barrier height of Ti/p-type InP Schottky diode with PANI interlayer was higher than that of the conventional Ti/p-type InP Schottky diode, implying that the organic interlayer influenced the space-charge region of the Ti/p-type InP Schottky junction. At higher voltages, the current transport was dominated by the trap free space-charge-limited current and trap-filled space-charge-limited current in Ti/p-type InP Schottky diode without and with PANI interlayer, respectively. The domination of trap filled space-charge-limited current in Ti/p-type InP Schottky diode with PANI interlayer could be associated with the traps originated from structural defects prevailing in organic PANI interlayer.

Carrier transport mechanism of Ni/Ag Schottky contacts to n-type GaN grown on Si(111) substrate

We fabricated Ni/Ag Schottky contacts to n-GaN grown on Si substrate and investigated its electrical properties using current–voltage characteristics measured in the temperature range of 200–400 K. The barrier height and ideality factor of Ag/Ni/n-GaN Schottky diode showed strong temperature dependence. The barrier height decreased and ideality factor increased, with decrease in temperature indicating a deviation from ideal thermionic emission. A barrier height of 1.00 eV was obtained for unity ideality factor from the linear relation between the obtained barrier heights and ideality factor. The lateral inhomogeneity of the Schottky barrier at the interface between Ni/Ag and n-GaN could be the main cause of temperature dependence of barrier and ideality factor and has been explained on the basis of thermionic emission with a Gaussian distribution of barrier heights. The electric field dependence of reverse current revealed that the Poole–Frenkel emission mechanism dominates the current transport in the reverse bias.

Modification of Schottky barrier properties of Al/p-type Si Schottky rectifiers with graphene-oxide-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) interlayer

The effects of graphene-oxide (GO) doping in the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) interlayer on the electrical and chemical properties of Al/p-type Si Schottky diodes were demonstrated. GO concentrations of 0.05 and 0.1 wt. % were used in the interlayer. The barrier height of the Al/p-type Si Schottky diode with a GO-doped PEDOT:PSS interlayer was higher than that of the diode with the pristine PEDOT:PSS interlayer; ultraviolet photoelectron spectroscopy measurements indicated that this could be well correlated with variations in the hole-injection barrier between the PEDOT:PSS interlayer and Al film caused by GO doping. The addition of 0.05 wt. % GO to the PEDOT:PSS interlayer increased the PEDOT to PSS ratio, resulting in an increase in conductivity. However, the conductivity of the PEDOT:PSS doped with 0.1 wt. % GO decreased; x-ray photoelectron spectroscopy results indicated that this could be attributed to the increased insulating GO content in PEDOT:PSS. At higher...

Stoichiometry-controlled growth of BaxSr1−xTiO3 thin films and their electrical behavior in heterojunction assemblies

We describe an optimized chemical synthesis route to obtain BaxSr1−xTiO3 (x = 0, 0.50, 0.67, 1.0) thin films with impeccable stoichiometry control. The molar ratios of the precursors were altered to produce the cubic phase of SrTiO3, Ba0.5Sr0.5TiO3, Ba0.67Sr0.33TiO3 and the tetragonal phase of BaTiO3 thin films on single crystalline p-Si (100) and quartz substrates. The obtained Raman spectra for the BaxSr1−xTiO3 thin films on quartz substrates showed characteristic vibration modes at ∼303, 515 and 716 cm−1. The active modes of BaTiO3 signify the tetragonal phase, which is important for its various technological advantages. The significant features of these materials were obtained through capacitance–voltage (C–V) measurements with Pt (or Ag)/BaxSr1−xTiO3/p-Si/Pt (or Ag) assemblies, at 1, 10 and 100 kHz. Substantial hysteresis (ΔV) of 315 mV (with Ag) and 219 mV (with Pt) was observed for Ba0.5Sr0.5TiO3, whereas for BaTiO3 and SrTiO3 the obtained hysteresis was 256 mV and 96 mV, respectively. The largest hysteresis of 793 mV was observed for SrTiO3 with a Pt electrode. The above findings are important for assessing the device compatibility of cost efficient solution processed BaxSr1−xTiO3 thin films.

Reverse leakage current mechanism in crystalline silicon solar cells with N+/P junctions

We have investigated the reverse leakage current mechanism of screen-printed Ag contacts on P-diffused crystalline Si solar cells of different efficiencies. The current-voltage measurements have been carried out in the temperature range of 175–450 K in steps of 25 K. The leakage current is independent of temperature for T< 300 K indicating the tunneling mechanism to be dominant at these temperatures in the cells of both efficiencies. The cell with higher efficiency exhibited higher leakage current compared to the lower efficiency cell as also evidenced by the lower activation energy obtained from the Arrhenius plot of reverse current. The higher leakage current in higher efficiency cell could be due to increased Schottky junction formation area compared to the lower efficiency cell.