B. Gürbulak

Growth and Temperature Dependence of Optical Properties of Er Doped and Undoped n-Type InSe

n-InSe and Er doped n-InSe (n-InSe:Er) single crystals were grown by the modified Bridgman-Stockbarger method. The prepared InSe and InSe:Er single crystal ingots were 12 mm in diameter and about 80 mm in length. The ingots had no cracks or voids on the surface. The absorption measurements were carried out for n-InSe, and n-InSe:Er samples in the temperature range of 10–320 K. Binding energies of n-InSe and n-InSe:Er were calculated to be 20.5 meV and 21.0 meV respectively. The direct band gaps were estimated to be 1.339 eV, 1.289 eV and 1.256 eV in n-InSe and were 1.338 eV, 1.288 eV and 1.253 eV in n-InSe:Er at 10 K, 200 K and 300 K, respectively. Eo (1.247 eV) obtained from the Urbach rule is nearly equal to the energy gap of n-InSe at 300 K.

Electric field influence on absorption measurement in InSe single crystal

Abstract InSe single crystal was grown by Bridgman–Stockberger method. Electric field effect on the absorption measurements have been investigated as a function temperature in InSe single crystal. The absorption edge shifted towards longer wavelengths and a decrease of intensity in absorption spectra occurred under an electric field of 5 kV / cm . Using absorption measurements, steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the Urbach energy. At 10 and 320 K , the first exciton energies were calculated as 1.350 and 1.311 eV for zero voltage and 1.334 and 1.301 eV for electric field respectively.

Growth and optical properties of Ho doped n-type indium selenide

n-InSe and Ho doped n-InSe (n-InSe:Ho) single crystals were grown by a method which is similar to the direct freezing method. The crystals used in this study were grown in our crystal growth laboratory. The ingots had no cracks and voids on the surface. There was no process to polish and clean the samples because of the natural mirror-like cleavage faces. The X-ray Laue back-reflection method was used to test the crystallinity of the prepared sample. The absorption measurements were carried out in n-InSe:Ho sample in the temperature range from 10 to 320 K. The exciton energies for n = 1 were calculated as 1.315, 1.302, 1.266 and 1.238 eV in n-InSe:Ho at 10, 100, 200 and 280 K, respectively. The exciton energies for n = 2 in n-InSe:Ho are 1.328, 1.322, 1.318 at 10, 60 and 80 K, respectively. The exciton binding energy of n-InSe:Ho was calculated as 17.3 meV. The direct band gaps for n-InSe:Ho are 1.332, 1.313, 1.283 and 1.255 eV at 10, 100, 200, 280 K, respectively.

Indium selenide: an insight into electronic band structure and surface excitations

We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at ~1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed.

The Advent of Indium Selenide: Synthesis, Electronic Properties, Ambient Stability and Applications

Among the various two-dimensional semiconductors, indium selenide has recently triggered the interest of scientific community, due to its band gap matching the visible region of the electromagnetic spectrum, with subsequent potential applications in optoelectronics and especially in photodetection. In this feature article, we discuss the main issues in the synthesis, the ambient stability and the application capabilities of this novel class of two-dimensional semiconductors, by evidencing open challenges and pitfalls. In particular, we evidence how the growth of single crystals with reduced amount of Se vacancies is crucial in the road map for the exploitation of indium selenide in technology through ambient-stable nanodevices with outstanding values of both mobility of charge carriers and ON/OFF ratio. The surface chemical reactivity of the InSe surface, as well as applications in the fields of broadband photodetection, flexible electronics and solar energy conversion are also discussed.

The Effect of Fe on the Absorption Spectra in TlGaS2, TlGa0.99Fe0.01S2 and TlGa0.98Fe0.02S2 Layer Single Crystals

TlGaS 2 , TlGa 0.99 Fe 0.01 S 2 and TlGa 0.98 Fe 0.02 S 2 single crystals were grown by the modified Bridgman-Stockbarger method. They did not have cracks and voids on their surface. The absorption measurements were carried out on TlGaS 2 , TlGa 0.99 Fe 0.01 S 2 and TlGa 0.98 Fe 0.02 S 2 samples in the temperature range 10-320 K with steps of 10 K. The phonon energies calculated for TlGaS 2 , TlGa 0.99 Fe 0.01 S 2 and TlGa 0.98 Fe 0.02 S 2 are (19.70 ± 5), (40.2 ± 5) and (15.1 ± 5) meV, respectively. The first and second defect levels have been found as 2.423 and 2.569 eV for TlGa 0.99 Fe 0.01 S 2 and as 2.017 and 2.426 eV for TlGa 0.98 Fe 0.02 S 2 at 10 K, respectively.

Absorption measurements in InSe:Ho single crystal under an electric field

InSe:Ho single crystal was grown by Bridgman-Stockberger method. Electric field effects on the absorption measurements have been investigated as a function of temperature in InSe:Ho single crystal. The absorption edge shifted towards longer wavelengths and a decrease of intensity in absorption spectra occurred under an electric field of 7.5 kV/cm. Using absorption measurements, steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the Urbach energy. At 10 K and 320 K, the first exciton energies were calculated as 1.322 and 1.301 eV for zero voltage and 1.245 and 1.232 eV for applied electric field, respectively.

The Growth of P-type TlGaSe2(1−x) S2x Single Crystals

TlGaSe2(1−x) S2x single crystals were grown by the modified Bridgman-Stockbarger method in our crystal growth laboratory. AIIIBIII C2VI compounds are formed of elements from vertical groups of the periodic table (group III: Tl, Ga, In; group VI: Se, S, Te) and are classified into two types. The first type has a layer structure: TlGaSe2, TlGaS2 and TlInS2. The second type has a chained structure: TlInSe2, TlInTe2 and TlGaTe2. None of the grown crystals had cracks and voids on the surface. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical or chemical polishing treatments. By the hot probe technique, we have found that the crystals were of p-type. The ingots produced were single crystalline and the useful region of single crystal was 90% with steps of 10 K if changes were small, and with steps of 3 and 5 K if changes were large in the direct and indirect band gaps energies. The direct and indirect band gaps for TlGaSe2(1−x)S2x samples were calculated as a function of temperature.

Electrical properties of Al/p–Ge and Al/Methyl Green/p–Ge diodes

Methyl green (MG) film has been grown for the first time on p–Ge semiconductor using a simple and low-cost drop coating method. The current–voltage (I–V) characteristics of Al/p–Ge and Al/MG/p–Ge diodes have been investigated in the temperature range of 20–300 K. A potential barrier height as high as 0.82 eV has been achieved for Al/MG/p–Ge diode, which has high rectification rate, at room temperature. It is seen that the barrier height of the Al/MG/p–Ge diode at the room temperature is larger than that of Al/p–Ge diode and ideality factor value of 1.14 calculated for Al/MG/p–Ge diode is lower than Al/p–Ge diode. The temperature coefficient of barrier height of the Al/MG/p–Ge diode has been calculated as 2.6 meV/K. The evaluation of current–voltage characteristics shows that the barrier height of the diode increases with the increasing temperature.

Electrical characterization of In/p-GaSe:Cd/Au–Ge single crystal grown by Bridgman/Stockbarger method

The temperature dependence of current–voltage (I-V) characteristics of Au–Ge/p-GaSe:Cd Schottky diode (SD) has been investigated in the temperature range of 40–360 K with a temperature step of 10 K under dark conditions. The characteristic parameters of the SD such as barrier height, ideality factor and series resistance have been determined from the I-V measurements. It has been shown that the ideality factor increases while the barrier height decreases with decreasing temperature. The values of series resistance obtained from modified Norde’s function. Series resistance values increase with decreasing temperature.