Proceedings of the Technical Session of Institute of Physics, Sri Lanka 12 (1996) c1

Grain Size Effects on the Reactivity of Copper Thin Films
C. R. Vithanage, J. K. D. S. Jayanetti and K. T. L. De Silva.
Department of Physics, University of Colombo, Colombo 3.

Copper, thin films were prepared on Ti plates by thermal deposition from thin cu wire. The deposition was carried out by varying distance between the source and the substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the morphological properties of the samples. A variation of grain sizes as a function of source to substrate distant was observed. Then the films were annealed at several temperature in the range of 200 0C to 700 0C. Effects of annealing in air have been studied using XRD and SEM. Reactivity was not observed during annealing below 2500C. However annealing above this temperature first produced cuprouse oxide and then cupric oxide. The temperature of oxide formation was observed to be decreased function of grain size.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 12 (1996) c2

Growth and Charaterization of Copper Indium Diselenide
B. D. Chithrani,¹, K. T. L. De Silva¹, J. K. D. S. Jayanetti¹and W. Siripala^2
1Department of Physics, University of Colombo, Colombo 3, ²Department of physics, University of Kelaniya, Kelaniya

CuInSe2 thin films were prepared on Ti plates by electrodeposition from an aqueous solution containing CuCl2, InCl3 and SeO2. The deposition was carried out at -0.5V Vs SCE. X-ray diffraction and Scanning electron microscopy have been used to study the crystallographic and morphological properties of the samples. Effects of annealing in air have also been monitored. Apparent bulk structure changes have been observed during annealing. Annealing of films at 350 0C was found to result in the formation of CuInSe2 films having a chalcopyrite structure, indicating that the samples are of good quality.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 12 (1996) c3

Type Conversion of Electrodeposited Cuprous Oxide
L. D. R. D. Perera¹, W. Siripala¹, K. T. L. De Silva²and J. K. D. S. Jayanetti^2
1Department of Physics, University of Kelaniya ²Department of Physics, University of Colombo

Cuprous oxide is an inexpensive and non-toxic semiconductor material having a direct band gap of 2.0 eV. In view of its possible applications in low-cost solar energy converting devices thin films were fabricated and their crystallographic and optoelectronic properties were investigated using X-ray diffraction and spectral response measurements.

Thin films of polycrystalline cuprous oxide were electrodeposited on indium tin oxide (ITO) coated glass substrates using an aqueous electrolyte under potentiostatic conditions. The photo-response of both the as deposited and annealed samples were investigated. The films were used in a three electrode photoelectrochemical cell for spectral response measurements. The experimental set up consisted of a potentiostat, a lock-in-amplifier, a monochromator and a chopper.

At rest potential, the photoresponse of the as deposited Cu2O films illuminated through the Cu2O/electrolyte interface (front illumination) was n-type in the whole spectral range. When illuminated through the ITO substrate (back illumination) the photocurrent was p-type for shorter wave lengths and n-type for longer wave lengths. These results indicate the existence of two n-type Schottky barriers at the Cu2O/electrolyte interface and at the Cu2O/ITO interface, and show that electrodeposited Cu2O thin films behave as an n-type material in a PEC cell.

The samples were annealed in air and their XRD patterns were obtained as a function of annealing. No significant change in the XRD spectra could be observed for samples annealed at temperatures below 300 0C. for samples annealed at temperatures above 3000C, the XRD spectra showed peaks corresponding to CuO and its complexes with water. Also, heat treatments at higher temperatures resulted in darker films.

In both the cases of front and back illuminations, the photoresponses of Cu2O annealed at 200 0C was n-type in the whole spectral range. When compared with the spectral response of the as deposited samples, these observations suggest that the Schottky barrier at the Cu2O/ITO interface has been removed by annealing at 200 0C. The films annealed at 300 0C showed a p-type photocurrent in the entire spectral range on front illumination. This observation suggests that the conductivity type of Cu2O has changed from n-type to p-type upon annealing at 300 0C.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 12 (1996) c4

A Deductive Approach in Introducing Quantum Mechanics to Undergraduates
G. Bandarage
The Open University of Sri Lanka, Nawala, Nugegoda

Distance techniques of teaching are used at the Open University where the student-teacher contact is minimal. Printed material comprises the main medium of instruction. The subject must be presented (a) in a logical order, (b) in simple terms and (c) in an interesting manner, for effective knowledge transfer. These three principles are applicable to face-to-face lectures delivered at a conventional University as well. However, they are more important in the distance mode of teaching. Also, one has to be mindful of the prejudices of the students against quantum mechanics.

At present the widely accepted and practised approach in introducing quantum mechanics is the historical or the inductive approach. This is well demonstrated by the fact that almost all the books on elementary quantum mechanics have adopted it. The flow of a typical presentation is as follows. (1) Quantization of electromagnetic radiation; Blackbody radiation, photoelectric effect and Compton effect. (2) Atomic spectra; the Bohr model. (3) Dual nature of subatomic particles; de Broglie hypothesis (4) Heisenberg uncertainty principle. (5) A heuristic deduction of the Schrodinger equation. (6) Postulates of quantum mechanics. It is argued that this approach has a number of undesirable feathers. As a remedial measure a deductive approach is suggested.

The flow in the deductive approach is as follows. (1) What is a theory and why do we need theories: Eliminates the need to store all the experimental results; Can predict the results of experiments not done yet; A particular theory is valid for a particular class of experiments. (2) Newtonian mechanics and its failure: What are postulates: Classical mechanics is based on three postulates: Does not work with sub atomic particles. (3) Peculiarities of the behaviour of subatomic particles; A Gedanken double slit experiment with bullets, waves and electrons. (4) Postulates of quantum mechanics.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 12 (1996) c5

I Watt, Quasi-CW, Diffraction Limited, Semiconductor Double Tapered Laser Oscillator
I.J. Dayawansa
Department of Electronic & Telecommunication Engineering, University of Moratuwa, Moratuwa

Semiconductor laser source are compact and convenient. They can be easily integrated with other semiconductor devices. They are useful as the source for free space communications between satellites; for optical radar and for pumping fibre amplifiers in optical fibre communication systems. They are also useful for many other applications.

For free space communications, a single frequency high power light source of narrow line width and large band-width is required. Coherent communication systems a high power source, with a single transverse mode and single longitudinal mode.

The narrow stripe laser can give a single mode output of a few hundred milliwatts of optical power. It cannot be pumped by more than a few milliamperes due to catastrophic optical damage to its facts. At high pumping levels, the narrow stripe laser shows optical saturation caused by very high optical power density. Naturally, a broad-area device would eliminate the above problems. However, they create the undesirable properties in the quality of the output. In other word, broad-area devices excite several modes in the near-field and in the far-field. Various researchers have been conducting theoretical and experimental work in the search of a single mode high power semiconductor laser source.

Work was carried out with home made bow-tie lasers and double tapered lasers using gallium arsenide quantum well material as shown in fig:1(a), (b) and (c). The light-current characteristics, the near-field and the far-field patterns were measured under quasi-CW conditions. Over 1W of optical power of wavelength 0.85mm, was produced at a current of 4A with double tapered laser oscillators. This is a power higher than what is so far reported from a semiconductor tapered oscillator. The near-field was gaussian below threshold. The far-field at high currents was a narrow single lobe but at lower currents, it had minor side