B. Abay

Interpreting the nonideal reverse bias C-V characteristics and importance of the dependence of Schottky barrier height on applied voltage

This work presents an attempt related to the charging behaviour of interface states to the nonideal forward bias current-voltage (I-V) and the reverse bias capacitance-voltage (C-V) characteristics of AlnSi Schottky barrier diodes. The diode showed nonideal I-V behaviour with an ideality factor of 1.50 and was thought to have a metal-interface layer-semiconductor configuration. Considering that the interface states localized at the interfacial layer-semiconductor interface are in equilibrium with the semiconductor, the energy distribution of the interface states was exactly determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height, θe. The determination of the intercept voltage and interface state density was made by means of a simple interface charge model which has been developed in detail. The I-V characteristics were used for determining the voltage dependence of the barrier height. Although the change in barrier height with applied biasis small, it is important for exactly determining the shape of the interface state density distribution curve. At a frequency of 500 kHz, the nonlinear reverse bias C−2−V plot with the curvature concave downward has been only thought of to be due to the contribution of the capacitance of the interface state charges. It is concluded that the nonlinear nature of C−2−V plots in the frequency range 50–200 kHz has been caused by the interface state charges as well as inversion layer and inversion layer charges. It has been understood by means of the interface state charge model that the C−2−V plots cannot only be interpreted in terms of the contribution of the interface state charges to the device capacitance.

Barrier characteristics of Cd/p-GaTe Schottky diodes based on I–V–T measurements

The current–voltage (I–V) characteristics of Cd/p-GaTe Schottky barrier diodes were measured in the temperature range 90–330 K. The apparent barrier height and the ideality factor derived by using thermionic emission (TE) theory were found to be strongly temperature dependent. Evaluating forward I–V data reveals a decrease of zero-bias barrier height (Φb0) but an increase of ideality factor (n) with decrease in temperature, and these changes are more pronounced below 150 K. The conventional Richardson plot exhibits nonlinearity below 150 K with the linear portion corresponding to an activation energy of 0.52 eV. The value of effective Richardson constant (A*) turns out to be 6.74 × 10−2 A K−2 cm−2 against the theoretical value of 119.4 A K−2 cm−2. It is demonstrated that the findings cannot be explained on the basis of tunnelling and image force lowering effects. Also, the concept of the flat-band barrier height (Φfb) fails to account for the temperature dependence of the diode parameters. Finally, it is demonstrated that these anomalies result due to the barrier height inhomogeneities prevailing at the metal–semiconductor interface. The inhomogeneities are considered to have Gaussian distribution with a mean barrier height of = 0.886 eV and a standard deviation of σs0 = 0.091 eV at zero bias. Furthermore, the mean barrier height and the Richardson constant values were obtained as 0.875 eV and 62.2 A K−2 cm−2, respectively, by means of the modified Richardson plot, ln(J0/T2) − (q2σ2s0/2k2T2) versus 1000/T. Hence, it has been concluded that the temperature dependence of the I–V characteristics of the Schottky barrier on p-type GaTe can be successfully explained on the basis of TE mechanism with Gaussian distribution of the barrier heights.

Temperature-dependent behavior of Ti/p-InP/ZnAu Schottky barrier diodes

The current–voltage (I–V) characteristics of Ti/p-InP Schottky diodes have been measured in a wide temperature range with a temperature step of 20 K. An experimental barrier height (BH) Φap value of about 0.85 eV was obtained for the Ti/p-InP Schottky diode at 300 K. A decrease in the experimental BH Φap and an increase in the ideality factor n with a decrease in temperature have been explained on the basis of a thermionic emission mechanism with the Gaussian distribution of the barrier heights due to the BH inhomogeneities at the metal–semiconductor interface. and A* as 1.01 eV, and 138 A cm−2 K2, respectively, have been calculated from a modified ln(I0/T2) − q2σ2s/2k2T2 versus 1/T plot. This BH value is in close agreement with the values of 0.99 eV obtained from the Φap versus 1/T and ln(I0/T2) versus 1/nT plots.

Current-voltage and capacitance-voltage characteristics of metallic polymer/InSe(:Er) Schottky contacts

Abstract An investigation of metallic polypyrrole polymer (MPP)/ n -InSe(:Er) (by an anodization process) Schottky barrier diodes (SBDs) fabricated on a cleaved n -type InSe(:Er) substrate, which is a layered semiconductor, has been made. The metallic polypyrrole film provides a good rectifying contact to the n- InSe(:Er) semiconductor. The current–voltage ( I – V ) and capacitance–voltage ( C – V ) characteristics of the diode have been determined at room temperature. The diode shows nonideal I – V behavior with an ideality factor greater than one. In addition, the I – V characteristics of the (MPP)/ n -InSe(:Er) device shows an improvement with an increased Φ b0 and a decreased ideality factor after the polymer melt processing step. The reverse bias C −2 – V characteristics of the diode shows a non-linear behavior.

Influence of temperature and phase transitions on the Urbach’s tails of absorption spectra for TlInS2 single crystals

Optical absorption spectra of TlInS2 single crystals were investigated in the temperature range of 10–340 K. The exponentially increasing absorption tails were explained as Urbach tails. TlInS2 single crystals exhibited five different convergent groups of lines ln α(E,T) having different convergence points of E0 and α0 between 120 and 340 K. Characteristic Urbach’s parameters such as steepness parameter [σ(T)], Urbach’s energy [Eu(T)], and effective phonon energy (hνp) were obtained as a function of temperature. σ(T) and Eu(T) exhibited a number of jump-like trends at the identified temperature regions. Jump-like changes of σ(T) and Eu(T) were explained to be due to the phase transitions (PTs) and contributions of electron–(exciton)–phonon interaction caused by exciton dissociation. The temperature dependence of the band gap (BG) exhibited six clearly distinct regions and differs from the temperature dependent BG behavior of known semiconductors. Absorption edge and band gap anomalies in TlInS2 samples at PT were interpreted using the theory proposed by Zametin [Phys. Status Solidi B 124, 625 (1984)]. Measured BG jumping values, ΔEgα, are greater than those calculated from this theory in the 340–200 and 175–120 K regions, while one of them is smaller than that of the calculated in the 198–180 K region. These differences were explained as due to PTs and simultaneous influence of phonon coupling with electrons (excitons) induced by exciton dissociation, and the existence of the chaotic states caused by the coexistence of different phases which have opposite sign contributions below the ferroelectric phase transition, respectively.Optical absorption spectra of TlInS2 single crystals were investigated in the temperature range of 10–340 K. The exponentially increasing absorption tails were explained as Urbach tails. TlInS2 single crystals exhibited five different convergent groups of lines ln α(E,T) having different convergence points of E0 and α0 between 120 and 340 K. Characteristic Urbach’s parameters such as steepness parameter [σ(T)], Urbach’s energy [Eu(T)], and effective phonon energy (hνp) were obtained as a function of temperature. σ(T) and Eu(T) exhibited a number of jump-like trends at the identified temperature regions. Jump-like changes of σ(T) and Eu(T) were explained to be due to the phase transitions (PTs) and contributions of electron–(exciton)–phonon interaction caused by exciton dissociation. The temperature dependence of the band gap (BG) exhibited six clearly distinct regions and differs from the temperature dependent BG behavior of known semiconductors. Absorption edge and band gap anomalies in TlInS2 samples at...

Excitonic absorption and Urbach-Martienssen's tails in Er-doped and undoped n-type InSe

Optical absorption spectra of InSe and InSe:Er single crystals were investigated just below and in the excitonic resonance energy region. The temperature dependence of the free exciton transition associated with the direct gap of InSe and InSe:Er were measured in the temperature range 10<T<340 K. The parameters describing the temperature variation of both the spectral position and the broadening function of the excitonic resonance confirm the dominating role of the average energy of crystal phonons. The Lorenzian lineshape was used to fit the excitonic structures. The increased absorption intensity and the narrowed lineshape of the excitonic resonances in InSe:Er crystals were attributed to the [Er] = 0.03 at% dopant atoms. The exponentially increasing absorption tail was explained as an Urbach-Martienssens (U-Ms) tail for both InSe and InSe:Er samples in the 100-340 K temperature range. The characteristic tail width, Urbachs energy EU, was obtained as a function of temperature. The temperature dependence of EU was interpreted based on the general models of this rule. The Urbachs energy decreased as a function of temperature in the temperature region investigated for the Er-doped sample. Such a decrease of the Urbachs energy can be explained to be due to the reduction of the electronic distortion caused by the structural disorders associated with the planar defects in the crystal lattice of InSe by the Er-doping procedure.

Electrical transport properties of p-GaTe grown by directional freezing method

p-type GaTe single crystals have been grown using the directional freezing method with different growth rates. Temperature-dependent Hall effect and resistivity measurements were carried out in the 80–325 K temperature range and at 1.6 T magnetic field. The free carrier concentration in the exhaust region was in the range of 9 × 1015–8 × 1016 cm−3 for growth rates of 3.3–0.39 µm s−1 and the hole mobility at 300 K ranged from 4.8 to 21 cm2 V−1 s−1. A systematic dependence of the hole carrier concentration and room temperature hole mobility on the growth rate was not observed. From temperature-dependent Hall measurements, we have found that the compensation ratio ND/NA was in the range of 0.39–0.69 regardless of the growth rate. The highest mobility of 342 cm2 V−1 s−1 at 100 K was achieved after annealing at 200 °C for 30 min. The fitting of the temperature-dependent free carrier concentration, using the single acceptor–single donor model, was used to determine the compensation ratio. Finding Nmax(m*)3/2 = 3.15 indicates high effective mass for holes or the possibility of a few close maxima of valence band edges with different effective masses.

Temperature dependence of galvanomagnetic properties for Gd doped and undoped p-type GaSe

The magnetoresistance and Hall effect measurements were carried out in undoped p-GaSe and Gd doped p-GaSe (p-GaSe:Gd) samples in the temperature range 90–320 K and 60–320 K, respectively. The transverse and longitudinal magnetoresistance coefficients for p-GaSe and p-GaSe:Gd samples decrease with increasing temperatures and were found to be MJ⊥B and MJ∥B∝T−2.37 (90⩽T⩽320 K) for p-GaSe and MJ⊥B and MJ∥B∝T−2.09 (60⩽T⩽320 K) for p-GaSe:Gd. The carrier concentration obtained from the Hall effect measurements in the p-GaSe:Gd sample increases up to 100 K, decreases in the range 100–140 K, increases in the range 140–280 K, and decreases in the range 280–320 K, although the carrier concentration in the p-GaSe sample continuously increases up to 320 K. Impurity energy levels calculated from ln(p/T3/2) vs 103/T for p-GaSe in the range 100–140, 140–220, and 220–320 K are Ec−216 meV, Ev +322 meV, and Ev +573 meV, respectively, and for p-GaSe:Gd in the range 100–140, 140–260, and 280–320 K are Ec−224 meV, Ev+330 meV,...

Barrier height enhancement by annealing CrNiCo alloy Schottky contacts on LEC GaAs

Abstract The Schottky barrier height and ideality factor of CrNiCo alloy Schottky contacts on a n -GaAs substrate have been measured using a current-voltage (I−V) technique after different rapid thermal annealings (RTA) for 20 s in a vacuum of ≈10 −5 torr (temperature range from 299 to 900 K). The value of barrier height Φ b and ideality factor n range from 0.57 eV at 1.14 (at room temperature) to 0.67 eV and 1.00 (at 673 K). Nonideal values of Φ b and n are attributed to the presence of an interfacial layer between the alloy and the semiconductor interface. However, the value of 1.00 for n at 673 K shows that annealing up to this temperature causes a disapperance of the I − V nonidealities. The fact that the barrier height increases and the ideality factor decreases to unity is ascribed to reduction of the interfacial oxide layer by metal Cr. On the other hand, the contact properties of the Schottky diodes deteriorated and became nearly ohmic when the annealing temperature reached 900 K for 20 s. This showed that there are not sufficient quantities of nickel in our CrNiCo alloy. The excellent saturation of the reverse bias curves which are due to the smoothness and quality of the metal/GaAs interface (even with annealing to a high temperature) are attributed to the existence of Co in the alloy.

Low-temperature photoluminescence of n-InSe layer semiconductor crystals

Abstract Low-temperature photoluminescence spectra of n-InSe layered single crystals were studied in the temperature range 10–210 K. Photoluminescence of n-InSe showed peaks at 1.334, 1.306, 1.288, and 1.232 eV at 10 K. These four peaks were attributed to radiative recombination of the direct free excitons, an impurity-band transition, a donor–acceptor recombination channel, and the transition within an impurity-vacancy complex, respectively. To determine the temperature dependence of direct band gap of n-InSe, we estimated the exciton binding energy to be 15 meV by assuming an isotropic approximation for the anisotropy parameter γ = 1. From these peak positions and the estimated band gap, the donor and acceptor levels associated with these centers were estimated to be approximately 43 and 18 meV, respectively. The temperature variations of the peak energy and linewidth of the excitons in n-InSe were explained by taking into account both the exciton–acoustic-phonon and the exciton–optical-phonon interactions. Below ≈60 K, these variations are due mainly to exciton scattering by acoustic phonons via the deformation potential in InSe.