No abstract

No abstract

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 ( b0 ) 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 f b 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 ¯ b0 = 0.886 eV and a standard deviation of σ s0 = 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(J 0 /T 2 ) − q 2 σ 2 s0 /2k 2 T 2 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.

No abstract

No abstract

No abstract

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-Martienssen's (U-M's) tail for both InSe and InSe:Er samples in the 100-340 K temperature range. The characteristic tail width, Urbach's energy E U , was obtained as a function of temperature. The temperature dependence of E U was interpreted based on the general models of this rule. The Urbach's energy decreased as a function of temperature in the temperature region investigated for the Er-doped sample. Such a decrease of the Urbach's 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.

Optical absorption spectra of GaSe and GaSe:Gd single crystals were investigated in the excitonic resonance energy region and just below. Free exciton (FE) transitions associated with the direct gap of GaSe and GaSe:Gd have been measured as a function of temperature in the range of 10-340 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 A (1) 1 homopolar phonon mode at 134.6 cm −1 . The Gaussian lineshape was used to fit the excitonic structures. The decreased absorption intensity and broadened lineshape of the excitonic resonances for GaSe:Gd crystals were attributed to the Gd dopant atoms. The exponentially increasing absorption tails were explained as Urbach-Martienssen (U-M) tails for both GaSe and GaSe:Gd samples in the 10-340 K temperature range. The characteristic tail width, Urbach's energy E U , was obtained as a function of temperature. The temperature dependence of E U was interpreted based on the general models on this rule. The Urbach energy increased as a function of temperature in the investigated temperature region for the Gd-doped sample. Such an increase of the Urbach energy can be explained as being due to the enhancement of electronic distortion caused by the structural disorder associated with the Gd atoms in the crystal lattice of GaSe.