Blue Room-Temperature Photoluminescence of AlN Films, Prepared by RF Magnetron Sputtering
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Blue Room-Temperature Photoluminescence of AlN Films, Prepared by RF Magnetron Sputtering V. Ligatchev, S.F. Yoon, J. Ahn, Q. Zhang, Rusli, K. Chew, S. Zhgoon School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Republic of Singapore ABSTRACT Photo luminescence (PL) signal from the aluminum nitride (AlN) films, excited by near UV (363.8 nm) laser has been measured at the room temperature. The AlN films are deposited by radio frequency (RF) sputtering of aluminum in argon-nitrogen-hydrogen gas mixture. Positions of the PL peaks maximums are influenced by the AlN preparation regimes. The analysis of the PL data is based on the results of the structural studies and electron spectrum investigations. INTROUDUCTION Light emitting in the blue area is important for the applications and has been extensively studied during the last decade [1 - 3]. Gallium and aluminum nitrides as well as GaN-based alloys are applied frequently for the blue-light devices producing, however preparation of the high quality layers is still quite expensive that limits of application areas of such devices [2 - 4]. Results of studies of AlN films, deposited by a radio frequency (RF) sputtering of aluminum (Al) target are presented in the paper. This technology allows to increase sufficiently the rate of the films growing with respect to the standard molecular-beam epitaxy or chemical vapor deposition processes. EXPERIMENTAL DETAILS Two series of aluminium nitride (AlN) films are obtained by RF (13.56 MHz, 300 W) magnetron sputtering of pure Al target in argon (Ar) and nitrogen-hydrogen (N2-H2) mixture on the ‘Denton’-18 sputtering system. Nominal substrate temperature (Ts) of 275 oC and Ar flow rate (FR) of 20 sccm are invariable for ‘a’ series whereas the N2+H2 mixture (N2:H2=95:5) FR is varied in the 4 – 40 sccm range. For the ‘b’ series the Ar and N2+H2 flow rates are equal to 10 and 5 sccm (respectively), N2:H2=80:20, the Ts value is changed from 600±50 to 900±50 oC. Standard substrate heater and substrate temperature control unit are used at the “a’ series deposition. A new heater was specially designed for the AlN films deposition at the relatively high substrate temperature. The heater current is only considered as a reliably controlled deposition parameter, while the Ts value is estimated indirectly for the sample of the “b” series. Nominally undoped (ρ > 20 Om*cm), single-side polished and oriented silicon plates are used as substrates. Typical films thickness is 0.3 – 0.5 µm for the “a” series and of 1.0 – 2.0 µm for the “b” series films. Spectra-Physics Beamlok 2065 Ar ion laser (363.8 nm wavelength, 40±2 mW) is used for the AlN photoluminescence (PL) excitation at the room temperature (293 K). Schematic diagram of the measurement system is shown on the figure 1. G5.11.1
Monochromator Cooling Water
Mirror
Ar+ laser
Photomultiplier
Monochromator
R2949
DK242
Sample Holder
Figure1. Schematic diagram of PL measurement system. The beam has a diameter of 1.5 mm. The PL of
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