Photoluminescence of mechanically polished ZnO

Abstract

The effects of mechanical polishing on the photoluminescence (PL) from each polar face of wurtzite-structure ZnO are presented. Differences observed for the 4.2K PL of a mechanically polished surface when compared to that of a chemomechanically polished surface include broadened bound-exciton peaks, hot-exciton luminescence, and a donor-acceptor pair peak at 3.2108eV. Analysis of this donor-acceptor pair peak results in estimated donor and acceptor ionization energies of 52±10 and 230±10meV, respectively, with a mean separation distance between pairs of approximately 3–4nm. The donors and acceptors are attributed to point defects introduced by dislocation motion during the polishing process and identified as octahedral Zn interstitials and Zn vacancies, respectively.

Cathodoluminescence study of ZnO wafers cut from hydrothermal crystals

“…These differences can arise from the crystal growth process itself, but also from the polishing step [6]. The concentration of the NRRCs is higher in the AFRL sample, as deduced from the significantly lower luminescence emission compared with the TD sample.…”

“…This strong variability suggests that it could be related to defects. In fact, its origin is a matter of controversy; it has been associated with the first LO phonon replica of the free exciton; it is 72 meV away the FXA exciton peak [6]; a donor acceptor pair (DAP) transition [16]; a free to neutral acceptor (e-A1) band [17]; from an exciton bound to extended defects (dislocations) [17]. Recent results around the Vickers indentations have revealed that this band is complex [18], and can consist of two subbands overlapping each other, peaking around 3.31 and 3.29 eV, respectively, which were associated with an exciton bound to a point defect, P D , and the one LO phonon replica of the free exciton, FX-1LO.…”

“…In spite of the progress achieved in ZnO crystal growth, (nowadays, high-purity large crystals are available [5]), many issues remain open to improve the wafer quality for homoepitaxial growth. One of the main points concerns the quality of the surfaces, which are very sensitive to machining presenting scratches and subsurface damage due to polishing [6]. On the other hand, the ZnO surfaces are very reactive, oxygen chemisorption being also a relevant issue [7].…”

Structural and optical properties of polar and non-polar ZnO films grown by MOVPE

“…In the non-polar materials, the high density of dislocations is responsible for the point defects as Zn vacancy (V Zn ) and oxygen interstitial (O i ) [22]. Ulrike also demonstrated the presence of point defects V Zn in non-polar ZnO materials by high-resolution scanning tunneling microscopy measurement [16].…”

Influence of dislocation decoration with mobile donors on exciton luminescence in ZnO crystals

“…The dependence of ZnO exciton luminescence on dislocation density is, therefore, an actual question, which is intensively studied [9−14]. In ZnO crystals, films and ceramics, such dislocation-induced effects as the quenching of initially present luminescence [9, 11−14] as well as the appearance of new luminescence bands [10,13] were observed. In the present paper, the influence of dislocations on ZnO room temperature exciton luminescence intensity and spectrum shape has been found.…”