LIF measurement of nitrogen metastable molecular state in a compact helicon plasma source

Summary form only given. There is a need for moderate energy fluxes of metastable nitrogen molecules in the growth of thin films of GaN, a wide band gap semiconductor. A laser induced fluorescence technique (LIF) has been developed for the measurement of N2 (A3 u + S , v=4) relative population density and flow speed in a steady state, helicon discharge at a pressure of 20 mtorr. This particular transition is part of the first positive system of N2 (3 3 A B u g + S reg P ). A coherent 899 tunable ring dye laser is scanned in the range 596.5-597.0 nm to pump the P12(9) rotational line of the (8,4) band of the A + Su 3 state to J=8 of the B3 g P state which then fluoresces by emitting a photon at 645.96 nm (the Q11(8) line of the (8,5) band). A Stanford Research SR830 lock-in amplifier and a 1 nm band pass interference filter in conjunction with optical chopping of the laser are used to distinguish fluorescent emission from spontaneously emitted background light at the same wavelength. A small portion of the laser light is passed through an iodine cell for a consistent zero-velocity reference measurement. With a calibration obtained by previous optical emission spectroscopy measurements and a model to account for reaction pathways in generation and destruction of 3 u A + S , it is possible to infer the density of this state. From the full width at half maximum (FWHM) of the Doppler broadened fluorescence line, the temperature of N2 molecules can be also inferred and compared with values of the gas temperature obtained by rotational analysis of ro-vibrational emission spectra of 1-0 an d 2-0 bands