The properties of mixed crystals of zinc-cadmium-sulphide(Zn(_x)Cd(_1-x)S)

CdS and ZnS are two binary compounds of II-VI semiconductors which form a continuous series of solid solutionsthroughout the whole range of composition (Zn(_x)Cd(_1-x)S). The main purpose of the work reported in this thesis was to characterise some electrical properties of Zn(_x)Cd(_1-x)S crystals grown in the department. Atomic Absorption Spectroscopy (AAS) was used to determine the actual composition of the solid solutions to compare with Energy Dispersive Analysis by X-Ray (EDAX) measurements. A calibration curve of ratio intensity versus composition can then be used to estimate thecomposition the X-Ray of Zn x Cdl -x S diffraction non-destructively. From the x-ray diffraction studies, all Zn(_x)Cd(_1-x)S crystals with x0.2, scattering due to ionised impurities, space charge or alloy processes is probably more important. The barrier heights of Au-Zn(_x)Cd(_1-x)S (x<0.5) Schottky diodes were calculated from forward I-V characteristics, C-V and photoelectric measurements were also carried out. A quite linear relationship with composition was observed for barrier heights measured by photoelectric method. Barrier heights calculated by the other methods was very much dependent on the nature of the barrier. From steady state photo capacitance studies, a level situated at about l.l-1.2eV above the valence band is the dominant feature for copper doped samples and crystals grown by the Piper-Polich method. This centre was pinned to the valence band. A second deep centre situated at about 1.4-1.5eV below the conduction band was also observed in some samples and was pinned to the conduction band. The existence of this centre is thought to depend very much on the history of the individual sample

Transmission properties of acousto optic material

Laser beam can be modulated by acousto optic modulator using a suitable acousto optic material. UV-VIS Spectrophotometer was utilized to investigate the transmission spectrum of two non linear acousto optic materials that are lithium niobate and fused quartz. From the spectrum it shows that transmittance for fused quartz and lithium niobate were 90% and 68% respectively. The absorption coefficient ? is calculated and plotted versus photon energy. It was found that ? increases linearly with photon energy in the range of 3.50 eV to 4.0 eV for fused quartz and 3.15 eV to 4.0 eV for lithium niobate. The estimated optical energy band gap was 2.97 eV for lithium niobate and 3.69 for fused quartz. From the transmission properties obtained in this study, it can be summarized that fused quartz is a better choice to be an acousto optic material

Laser beam modulation by an acousto optic mode locker

Nazariahmatdaud2006the characterization of beam modulation by acousto-optic mode locker is reported. Hene laser was employed as a source. Acousto-optic mode locker (aoml) was used to convert the continuous beam to become pulsed. Radio frequency signal provided an acoustic source to the aoml. The signal was amplified using a power amplifier. A pulse generator was utilized to regulate the frequency of the signal. The frequency and the power of the amplifier were varied to characterize the modulated beam. The hene laser beam was modulated into a periodic signal. The pulse width of the modulated signal was found to increase linearly with the rf pulse width. The modulated signal intensity was also found to vary linearly with rf drive power_laserbeammodulationbya

Reliability study of silicon carbide Schottky Diode with fast electron irradiation

The impact of fast electron exposure upon the performance of commercial silicon carbide Schottky diodes has been studied. Under 3 MeV electrons, absorbed dose of 10 and 15 MGy at room temperature, the forward current density-voltage characteristic of INFINEON and STMICROELECTRONICS devices have been decreased by 4.6 and 8.2 orders of magnitude respectively. The reduction is associated with the significant rise in the series resistance (INFINEON: 1.45 Ω to 121×103 Ω; STMICROELECTRONICS: 1.44 Ω to 2.1 × 109 Ω) due to the irradiation-induced defects. Besides that, the reverse leakage current density in INFINEON increased by one order of magnitude while reverse leakage current density in STMICROELECTRONICS decreased by about one order of magnitude. We have also observed an increase in ideality factor (INFINEON: 1.01 to 1.05; STMICROELECTRONICS: 1.02 to 1.3) and saturation current (INFINEON: 1.6×10-17 A to 2.5×10-17 A; STMICROELECTRONICS: 2.4×10-15 A to 8 × 10-15 A) as a result of electron irradiation. Overall, for particular devices studied, INFINEON have better quality devices and more radiation resistance compared to STMICROELECTRONICS

Optical properties of Ti:Al2O3 single crystal

Optical transmission and absorption spectra of Ti:Al2O3 single crystal have been determined in the region of UV-vis and infrared at room temperature. The main absorption peaks at 491 nm and 562 nm, the weak infrared absorption band at 650 nm and the strong UV absorption band below 300 nm are observed. The absorption coefficient alpha was determined in the visible range while the optical band gap have been determine using the relation of alpha 1/2 vs (hv) plot. The refractive index is discussed in the vicinity of Fresnel's equation. In particular, the Sellmeier equation was determined in the range visible region by means on non-conventional method based on the measurement of refraction by using UV-visible spectroscopy. The refractive indices are forward to decrease from 3.71 to 1.28 in the wavelength range 400 - 800 n

Study the absorption of diode pumped solid state laser on Ti: sapphire crystal

Exciting laser material is a challenging task. Only certain source is appropriate to pump the electron to an excited state. This depends on how much the pumped source will absorb and cause the fluorescence. Hence, this research was carried out to estimate the percentage of energy absorbed in the laser material. In this case, ti:sapphire crystal was employed as an active medium. High power diode laser was used as a pumping source. A powermeter was utilized to measure the output of the beam. The absorbance power was estimated to be 1.29 w from the result of transmission and reflection measurement

Titanium doped sapphire crystal excited by diode pumped solid state laser

The laser crystal emission property is the crucial factor to produce laser. An appropriate pumping source is needed to pump atom in the crystal to an excited state which depend to the absorption band of the crystal. The emission only occurs when the threshold value is exceeded. The aim of this research is to study the absorption and emission spectrum of the laser crystal during pumping process. Ti:sapphire crystal was employed as an active medium. High power diode pumped solid state (DPSS) laser was used as a pumping source. A spectrum analyzer was utilized to detect the absorption and emission spectrum of the crystal. The absorption spectrum comprised of 532.01 nm, 807.23 nm and 1064.07 nm. The major of emission spectrum is 806.80 nm with intensity achieved up to 97.46 %. The optimum emission was occurs at corresponding pumping current of 22 A

Experimental study of thermoelectric cooler for diode pumped solid state laser

Thermoelectric cooler (tec) is a solid state heat pump. It normally used for a diode pumped solid state (dpss) laser. It is used to control and stabilize the temperature of pumping source of laser diode (ld) and the frequency doubled of kalium titanyl phosphate (ktp) crystal. The aim of this study is to diagnose the performance of tec in dpss system. High power laser diode driver circuit was utilized as a pumping source. The current of the driver circuit was verified and the temperature of the ld and ktp were measured. The result obtained indicates that, the temperature of ld linearly increased upon the current in the initial stage. After achieving a threshold current of 7 a the temperature remained constant at 25.4 oc. Unlike in ktp crystal, initially the temperature was nonlinearly decreased down to the minimum of 14.8 oc at threshold current. The temperature was then nonlinearly increased up to maximum of 25.7 oc at 15 a. Beyond 18 a, the temperature slightly dropped and remained constant at the same value of ld temperature of 25.4 oc. Hence the tec was stabilized and controlled the temperature of dpss laser at 25.4 oc. The best performed of tec when the pumping current exceeds 18

Silicon carbide schottky diodes forward and reverse current properties upon fast electron radiation

This paper investigates on the reaction of 10 and 15MGy, 3MeV electron irradiation upon off-the-shelves (commercial) Silicon Carbide Schottky diodes from Infineon Technologies (model: IDH08SG60C) and STMicroelectronics (model: STPSC806). Such irradiation reduces the forward-bias current. The reduction is mainly due to the significant increase of the series resistance (i.e. Infineon: 1.45Ω at before irradiation → 121×103 Ω at 15MGy); STMicroelectronics: 1.44Ω at before irradiation → 2.1×109 Ω at 15MGy). This increase in series resistance gives 4.6 and 8.2 orders of magnitude reduction for the forward-bias current density of Infineon and STMicroelectronics respectively. It is also observed that the ideality factor and the saturation current of the diodes increases with increasing dose (i.e. ideality factor- Infineon: 1.01 at before irradiation → 1.05 at 15MGy; STMicroelectronics: 1.02 at before irradiation → 1.3 at 15MGy | saturation current- Infineon: 1.6×10-17A at before irradiation → 2.5×10-17A at 15MGy; STMicroelectronics: 2.4×10-15A at before irradiation → 8×10-15A at 15MGy). Reverse-bias leakage current density in model by Infineon increases by one order of magnitude after 15MGy irradiation, however, in model by STMicroelectronics decreases by one order of magnitude. Overall, for these particular samples studied, Infineon devices have shown to be better in quality and more radiation resistance toward electron irradiation in forward-bias operation while STMicroelectronics exhibit better characteristics in reverse-bias operation