Universal Journal of Materials Science 7(3): 35-41, 2019 DOI: 10.13189/ujms.2019.070301 http://www.hrpub.org Effects of Transition Energy on Intra-Band Photoluminescence of Zinc Oxide (ZnO) Semiconductor under Low injection Level Getu Endale Department of Physics, CNCS, Wolkite University, P.O.Box 007, Wolkite, Ethiopia Copyright c 2019 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract This paper presents the effects of the transition energies on photoluminescence intensities in Zinc Oxide compound semiconductor due to the intra-band transition of free carriers. The excitation of free carriers from the valence band to conduction band and from different localized state to the conduction band by the illumination of sufficient energy is considered. A theoretical model for minority carrier trapping is also investigated to explain the dependence of the photoluminescence on the trap energy. Variation of photo- luminescence intensities along with localized state energy and transition energy is considered at different temperatures. As temperature increases the photoluminescence due to the transition of free electrons from the conduction band to the valence band, from the conduction band to the localized states and from the localized states to the valence band are increasing. Keywords Photoluminescence, Intra-band, Photon Energy, Energy Bands. 1 Introduction For different semiconductor devices, one needs materials with different parameters, like energy band-gap. Physical properties are very different among different semiconductors due to distinct characteristics of energy band-gaps and impu- rities. These impurities play a major role in determining the electrical and optical properties of semiconductors. Almost all of today’s technology involves the use of semiconductors, with the most significant aspect being the integrated circuit (IC). One of the most commonly used techniques to investigate the properties of semiconductors is Photoluminescence (PL). PL has become a standard method for the characterization of semi- conductor properties. It can be used to determine energy levels, concentration of impurities, defects and fundamental proper- ties of semiconductors [1]. ZnO is a typical II-VI semiconductor material with a wide band gap of 3.37 eV, intrinsic carrier concentration (< 10 6 cm -3 ) (max n-type doping (> 10 20 cm -3 ) electrons; max p-type doping 10 17 cm -3 holes), exciton binding energy 60meV , electron 0.24 and hole effective mass 0.59 respec- tively at room temperature. In direct band gap the electron may be excited without the assistance of a phonon and can be seen as a more abrupt absorption edge in the spectra. Differ- ent materials are also classified by the magnitude of their band gap energy into one of three categories: narrow-band gap, mid band gap, and wide-band gap. There has been notable interest in the use of wide band gap semiconductors for consumer as well as defense applications [2, 3, 4, 5, 6, 7]. Photoluminescence involves the irradiation of the crystal to be characterized with photons of energy greater than the band- gap energy of that material. Photoluminescence consists of impinging relatively high frequency light onto a material, ex- citing atomic electrons. Subsequent relaxation may result in the production of photons that are characteristic of the crys- tal or defect site that emits the light. The luminescent signals detected could result from the band-to-band recombination, in- trinsic crystalline defects (growth defects), dopant impurities (introduced during growth or ion implantation), or other ex- trinsic defect levels (because of radiation or thermal effects) [8]. Photoluminescence (PL) is the spontaneous emission of light from a material under optical excitation. PL measure- ment is a kind of powerful and nondestructive technique, which has been carried out on most of semiconductors. When light of sufficient energy is illuminated a material, photons are ab- sorbed and excitations are created. These excited carriers re- lax and emit a photon. Then PL spectrum can be collected and analyzed. However,the absorption can happen in materi- als, only when the energy of photon is equal to or higher than the band gap. Therefore, we have to choose different excitation source to do the measurements according to different material with different electronic band structure. The PL peak positions reveal transition energies and the PL intensity implicates the relative rates of radiative recombination [9]. From PL mea- surement, we can obtain a variety of material parameters, such