Growth temperature and N2 ambient pressure-dependent crystalline orientations and band gaps of pulsed laser-deposited AlN/(000 1) sapphire thin films

• Published in: Journal of crystal growth Vol. 304; no. 1; pp. 257 - 263
• Main Authors: JEJURIKAR, Suhas M, BANPURKAR, A. G, BANKAR, Deepak N, ADHI, K. P, KUKREJA, L. M, SATHE, V. G
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 01.06.2007
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Materials science; Methods of crystal growth; physics of crystal growth; Methods of deposition of films and coatings; film growth and epitaxy; Other semiconductors; Physics; Specific materials; Surface and interface electron states; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Theory and models of film growth; Temperature dependence; Atomic force microscopy; Electronic properties; Pressure effects; Crystal orientation; A3. Thin films; Pulsed laser deposition; 81.15.Fg; Raman spectroscopy; Preferred orientation; Thin films; Energy gap; Sapphire; Optical properties; Aluminium nitrides; Growth mechanism; A3. Laser processing; B2. Semiconductors; 68.55.Jk; 81.70.Fy; III-V semiconductors; Crystal structure; 81.05.Ea
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2007.02.004

We report a study on the role of substrate temperature (Ts), ranging from 850 to 1150 deg C and the effect of ambient nitrogen pressure (5X10-4 and 5X10-5Torr) on the structural and optical properties of pulsed laser deposited AlN thin films on c-axis Al2O3 substrates. It is found that along with the band gap of the pulsed laser-deposited AlN thin films, the crystallographic orientation turns from to (0002) depending on the substrate temperature (Ts) and the ambient nitrogen pressure. At Ts=850 deg C and above-mentioned nitrogen pressures, the deposited thin films showed preferential orientation along and a band gap of about 5.4eV. At higher Ts of 950 deg C, both the orientation i.e. and (0002) were observed. The variation in intensity of these orientations depends on the ambient nitrogen pressure. At 5X10-4Torr, both the orientations were observed with almost equal proportions and the band gap of the corresponding thin film was about 5.4eV. Interestingly, at lower pressure of 5X10-5Torr the film, predominantly, showed orientation along (0002) and the band gap of the corresponding film was about 5.9eV. At even higher Ts=1050 deg C, even though the films were oriented mainly along (0002), the crystalline quality of the films deposited at 5X10-5Torr nitrogen pressure was much superior when compared to those deposited at 5X10-4Torr nitrogen pressure. Investigations of the thin films using atomic force microscopy and Raman spectroscopy support the above observations. Attempts have been made to explain the observations in terms of the temperature and pressure-dependent growth modes.