Y K Yogurtçu

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.

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.

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,...

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.