Growth Kinetics of GaN Thin Films Grown by OMVPE Using Single Source Precursors
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ABSTRACT We report the growth kinetics of GaN thin films using the single source precursor bisazido dimethylaminopropyl gallium (BAZIGA) in a cold wall reactor. Transparent, smooth, epitaxial (FWHM of the α-GaN 0002 rocking curve = 129.6 arcsec) and stoichiometric GaN films were grown on c-plane Al2O3 substrates in the temperature range of 870 – 1320K and high growth rates were obtained (up to 4000 nm/hr). Film growth was studied as a function of substrate temperature as well as reactor pressure. Although high quality films were obtained without using any additional source of nitrogen such as ammonia, we have investigated the effect of ammonia on the growth and properties of the resulting films. The films obtained were characterized by XRD, RBS, XPS, AES, AFM, SEM and the room temperature PL spectroscopy of GaN films grown exhibited the correct near band edge luminescence at 3.45 eV.
INTRODUCTION The nitrides GaN, AlN, InN and their ternary alloy systems AlGaN and InGaN are very promising materials for applications in green/blue light-emitting diodes and semicon-ductor lasers[1]. The commercial growth of high quality epitaxial group-13 nitrides by organometallic vapor phase epitaxy (OMVPE) is based on the co-pyrolysis of metal alkyls MR3 (M = Al, Ga, In, R = CH3, C2H5, tBu) and NH3. But high temperatures are involved in this process for the effective activation of NH3 (>773K for InN[2], >1173K for AlN and GaN[3]). Many efforts have been undertaken to substitute the ineffective nitrogen source (NH3) using alternative precursors based on the concept of preformed direct M-N bonds in the precursor molecule. Such precursors for the growth at a lower V/III ratio and milder growth conditions were achieved with many compounds for instance hydrazine (N2H4), 1-1-dimethyl hydrazine (M2NNH2), phenyl hydrazine (PhNH-NH2), hydrazoic acid (HN3)[6-8] and also alkyl amines (RNH2, R = tBu, iPr)[9]. But the disadvantages of these precursors are their toxic and explosive nature as well as carbon incorporation into the resulting films. Besides these compounds, some group-III metal amido compounds such as [R2GaNH2]3 (R = Et, Me) and [Ga(NR2)3]2 (R = Et, Me) are interesting as single source precursors (SSP). However these precursors are only used with limited success in terms of the achieved film properties[10]. The azides such as [R2GaN3]x (R = Cl, H, Et, Me) are possible candidates as SSP and have been already used successfully to grow GaN[11]. The azide group combines a pre-formed strong Ga-N bond with a reduced number of undesired Ga-C and N-C bonds to minimize the carbon incorporation during film growth. But the disadvantage with these precursors are their air sensitivity and explosivity. To find an alternative to these problems we concentrated our research on the growth
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of epitaxial GaN films using the novel Lewis-base stabilized organometallic azide compound of the type (N3)aM[(CH2)3NMe2]3-a (M = Al, Ga, In and a = 1, 2). These SSP’s are non-pyrophoric, non-explosive and yield epitaxial GaN films under moderate conditi
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