V. A. Kheraj

Barrier inhomogeneities in Au/CdSe thin film Schottky diodes

Schottky diodes have been fabricated by depositing Au on n-type CdSe thin films using the thermal evaporation technique, and their properties have been investigated by current–voltage and capacitance–voltage measurements. At room temperature, the characteristics obey the pure thermionic emission theory and the barrier height has been found to be 0.63 eV. The barrier heights decrease, while ideality factors increase with decrease in temperature. Further, the activation energy plot does not provide the expected Richardson constant and barrier height values. The abnormal behavior of the barrier heights and the ideality factors with respect to temperature as well as the difference between the barrier heights measured from I–V and those from C–V or flat band have been explored on the basis of barrier height inhomogeneities.

Studies on Zinc Oxide Nanorods Grown by Electron Beam Evaporation Technique

Nanocrystalline zinc oxide-thin films have drawn the attention of researchers due to its attractive properties like transparency in visible region, abundance in nature and gas sensitivity. Nanostructured Zinc oxide (ZnO) thin films were grown on silicon, alumina and glass substrates at various substrate temperatures using a 6 kW electron beam evaporation technique. The effects of film thickness, growth temperature and substrate on the crystallinity of deposited ZnO films were investigated using X‐ray diffraction, scanning electron microscopy, optical absorption and photoluminescence studies. Our studies show that good quality films are obtained for silicon substrate for a growth temperature of 250°C. Film thickness plays an important role on the evolution of the nanostructures. SEM studies combined with XRD analysis reveal that ultrathin nanorods are grown with (002), (101) and (102) orientations. All the ZnO films show room temperature photoluminescence emission bands at 394 nm and 468 nm. Optical absorption studies show strong absorption at 377 nm. Details of the structure and optical properties correlation will be presented and potential of a simple technique such as e‐beam deposition to grown ZnO nanostructures suitable for optoelectronic application will be assessed.

Effect of facet reflectivities on high-power highly strained InGaAs quantum-well diode lasers operating at 1.2 μm

The power enhancement of laser diodes is achieved by single and multilayer facet coatings such as antireflection and high reflection respectively at the front facet and the back facet of the laser diode. In this work, we have experimented with single layer λ/4 thick Al2O3 film for the Anti Reflection (AR) coating and stack of λ/4 thick Al2O3/ λ/4 thick Si bi-layers for the High Reflection (HR) coating. The AR/HR coatings were deposited in an electron beam evaporation system. The effect of front and back facet reflectivities on the output power of diode laser has been studied. The highly strained MOVPE grown InGaAs quantum-well edge emitting broad area (BA) diode lasers have been used for this experiments. The light output versus current (L-I) measurements were made on selected devices before and after the coatings. The devices were tested under pulsed operation with a pulse width of 400 ns and a duty cycle of 1:400. We have also carried out the theoretical analysis and simulation of L-I characteristics for this particular diode structure using LabVIEW. The experimental results were compared with simulated results. The effect of facet coating on external differential efficiency of diode laser has also been studied.

Simple Low-Cost Technique for in-Situ Reflectivity Monitoring of Optical Thin-Films and its Application in Laser Diode Facets-Coating

Laser diodes are by far the most varied, flexible, cheapest and the most abundant lasers. For long-term, reliable operation and for maximum optical power utilization, laser diode is coated with the anti-reflection (AR) and high-reflection (HR) coatings by means of dielectric layers on the front and the back facet, respectively. For the optimum performance, accurate monitoring and control over the reflectivity of the dielectric thin film layers at specific lasing wavelength is necessary. We have demonstrated a simple and inexpensive in-situ reflectivity measurement system for the facets-coating of laser diodes. The system relies on the measurement of dynamic optical reflectance of the growing thin film by means of intensity of a laser-beam reflected from the gallium arsenide test-substrate kept in the close vicinity of the laser diode facet being coated. The in-situ reflectivity monitoring of single layer AR film and multilayer HR films have been demonstrated and verified with ex-situ reflectivity measurements.