Spectrally Resolved Cathodoluminescence (SRCL) of Hydrothermal ZnO crystals
- PDF / 368,836 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 186 Views
Y1.7.1
Spectrally Resolved Cathodoluminescence (SRCL) of Hydrothermal ZnO crystals J. Mass1,4, M. Avella1, J. Jiménez1,. M. Callahan2, E. Grant2, K. Rakes2, D. Bliss2;. Buguo Wang3, 1
Física de la Materia Condensada, ETSII, 47011 Valladolid, Spain Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731, USA 3 Solid State Scientific Corporation, Hollis, NH 03049, USA 4 Dpto. Matemáticas y Física, UniNorte, Km 5 Barranquilla, Colombia 2
ABSTRACT Large hydrothermal ZnO crystals were grown using 3N NaOH, 1N KOH and 0.5N Li2CO3 mineralizer. The crystals were studied by cathodoluminescence (CL), showing a good crystalline quality. Different growth regions were identified by CL imaging. These regions were characterized by their corresponding luminescence spectra, showing that the incorporation of impurities and non radiative recombination centers depend on the growth sector. The surface is shown to introduce band tailing modifying the high energy part of the spectrum. The main spectral signatures of each sector are discussed.
INTRODUCTION ZnO is emerging as a material with high potential for optoelectronic applications. Its large bandgap (3.4 eV) and large free exciton binding energy (60 meV) make it an excellent candidate for blue and UV devices (1). In relation to III-nitrides it presents the advantage that large crystals can be grown, enabling homoepitaxial growth on substrates of high crystalline quality desirable for long life devices. In this context, large crystals free of defects are necessary to boost the development of ZnO based optoelectronics. ZnO crystals can be grown by different methods, vapor phase transport (VPT) (2), melt (3) and hydrothermal (HTT) (4). The quality of the crystals needs to be further improved in order to be suitable for high quality homoepitaxial film growth. HTT presents some advantages with respect to the other methods, since it allows growth of low dislocation density down to ≈102 cm-2. However, problems regarding the incorporation of impurities and native defects remain critical for the development of high quality hydrothermal ZnO crystals. The hydrothermal growth of ZnO requires a mineralizer containing alkaline metals, Li, Na and K, which are known to introduce levels in the band gap affecting the optical properties of the crystals. The origin of the different luminescence emissions in ZnO remains a matter a controversy. Its understanding is crucial for the control of the impurities in these crystals. We present herein a spectrally resolved cathodoluminescence (CL) study of hydrothermally grown ZnO crystals; the main factors affecting the luminescence emission and its distribution are discussed. EXPERIMENTAL AND SAMPLES Hydrothermal growth of ZnO crystals is carried out in stainless steel autoclaves. To avoid iron contamination a platinum inner capsule is used. Usually, large HTT ZnO crystals are grown in 210 molal alkali solutions at temperatures between 200 and 500ºC and pressures between 500 and 2000 bars. The ZnO seeds are cut in the desired orientation, a
Data Loading...
