الفهرس 
Cover EnglishOnly 14 pages are availabe for public view
 |  | from | 149 |  |  |
| | | from | 149 | | |
Abstract
This present work is dealing with different techniques used in examining semiconductors; optical characterization was performed on bulk crystals from ZnSe, ZnTe and ZnSexTe1-x where 0 x 0.202, and the samples used here were grown from the melt.Low-Temperature Photoluminescence (PL) spectra were measured on six samples, the spectra of ZnSexTe1-x showing a broad band which may be attributed to self activated emission. The broad self activated(SA) emission band have been assigned to various crystalline defects, such as dislocations and vacancies or their combination with impurities The PL emission intensity increases at low temperatures due to the lack of thermally excited phonons, the emission spectrum remained broad even at low temperatures. DAP is observed about 2.3 eV at x=0, 0.048, 0.202. Raman spectra of ZnSexTe1-x crystals were measured at room temperature, moreover the temperature dependence Raman spectra of ZnSe were considered in the temperature range 77 K to 358 Ko. Room temperature Raman spectrum of ZnSe single crystal which showed peaks at 140.8, 208 , 251.2 cm-1,which could be assigned to 2TA, TO, LO respectively. In order to account for the effect of substitution of Se by Te on the Raman bands we considered samples of the type ZnSexTe 1-x having x=0, 0.038, 0.048, 0.166, 0.202 and 1 where x is the percent of selenium, the LO mode of pure ZnTe changes into the LO mode of pure ZnSe with increasing Se content and the TO mode of ZnTe changes into the TO mode of ZnSe. This behavior is called single or one-mode behavior. Current-voltage (I_V) characteristics of ZnSexTe1-x samples sandwiched between Ag layers were measured; Experimental results proved that Ag makes ohmic contacts with ZnSexTe1-x bulk samples where x ranged from 0 to 1.The room temperature photoelectric response spectra of ZnSexTe1-x samples (0 x 1) were measured, the spectra are characterized by a single band situated in the and edge region. This can be attributed to the generation of more number of free charge carriers in the band gap region. The experimental results of the band gap determined from the photoconductivity spectra at room temperature were compared with the theoretical results obtained from Vegard’s law Eg(x) =2.26-1.238x+1.648x2 Studying the kinetics of photoconductivity, we determined the relaxation time (or the carrier life time) and we get the life time of the carriers in ZnSexTe1-x crystals in the range of a few milliseconds. Using hot probe method, where we concluded that ZnSe single crystal is p type but the polycrystalline ZnSexTe1-x are of n type. A good accordance was noticed between the results and conclusion obtained here using different experimental techniques: PL Spectroscopy, Raman spectroscopy, photoconductivity and Energy Dispersive X-ray analysis confirmed the chemical composition of ZnSexTe1-x.