THE OPTICAL PROPERTIES OF ZnO:Al FILMS DEPOSITED ON THE (0001) SURFACE OF ε-GaSe SINGLE CRYSTALS

ZnO:Al-GaSe:Cd heterojunctions were obtained by the thermal treatment of Cd-doped GaSe lamellae covered with a Zn nanometric layer containing different Al concentrations. The heterostructures were structurally (XRD) and optically (reflection spectra and dielectric permittivity for 1.5÷5.0 eV) analyzed. 1. Introduction Heterojunctions based on A III B VI stratified semiconductors and their (A III B VI ) oxides, as well as oxide heterojunctions with I-II group metals optically transparent in a wide wavelength region, occupy a special place in the physics of semiconductor devices. The weak cohesion between the packings allows the cleavage of the single crystals as lamellae (parallel planes) having perfect surfaces at the atomic scale. This property, along with low concentration of the surface density of states, classify these materials as ideal objects for the elaboration of a large variety of optoelectronic devices, such as detectors of ionizing radiation, photodiodes, photovoltaic cells, and many other [1-6]. The photosensitivity curve of gallium monoselenide steeply decreases in the blue-violet spectral region regardless of the high structural quality of the surface [7]. A nanometric own oxide layer deposited in-between optical window electrode (In2O3) and the semiconductor results in the increase of the photosensitivity in the green-violet spectral region [8]. Multiple investigations carried out recently unambiguously demonstrate that the physical properties of the structures based on A III B VI stratified semiconductors are mostly determined by the type and characteristics of the optically transparent oxide [9, 10]. Zinc oxide, being polycrystalline, undoped and doped with low Al concentrations is a highly conductive material [7], and it is optically transparent in the visible spectral region [11]. ZnO has a certain amount of properties widely used in various devices (acoustic cells, varistor, gas sensors, etc. [12-17]). Nanocrystalline ZnO layers obtained by various technologies (spray pyrolysis, CBD, pulsed laser deposition, CVD, etc.) have a good adhesion to the surface of semiconductor or dielectric substrates. This fact is widely used in optoelectronic and solar energy conversion devices [15], photodetectors of UV radiation [16] and sources of laser radiation [17]. The characteristics of the devices based on ZnO and ZnO:Al are highly influenced by the properties of semiconductors used as a substrate. This paper presents the investigations on some optical properties of nanometric ZnO doped with aluminium (0.05÷5.0 at %) deposited onto GaSe substrates.