Synthesis and characterization of single precursors for growth of MN (M = Al, Ga) thin films

Abstract

Reactions of trialkylaluminum and trialkylgallium with 1,1-dimethylhydrazine afford respective dimeric $[R_2M-μ-N(H)NMe_2]_2$ (1, M = Al, R = Me; 2, M = Al, R = Et; 3, M = Ga, R = Me; 4, M = Ga, R = Et) as a mixture of trans and cis isomers. Variable-temperature $^1H$ NMR studies show that 1 ~ 4 undergo fast trans-cis isomerization with free enthalpy of activation ($ΔG^‡_c$), 9.3 kcal/mol for 1, 8.8 kcal/mol for 2, 15.6 kcal/mol for 3, and 15.3 kcal/mol for 4. The trans-cis isomerizations have not been affected by Lewis bases such as pyridine and 4-methylpyridine, implying that the $NMe_2$ moiety in 1 ~ 4 acts as an internal base to facilitate the isomerization. Trimeric amidogallanes, $[R_2Ga-μ-NH_2]_3$ (5, R = Me; 6, R = Et), have been isolated by treatment of trialkylgallium with ammonia. Reactions of 5 and 6 with 1 equiv of hydrogen azide afford respective monomeric $R_2(N_3)Ga:NH_3$ (7, R = Me; 8, R = Et). The ammonia ligand in 7 and 8 can be quantitatively substituted by t-butylamine to produce $R_2(N_3)Ga:NH_2^tBu$ (9, R = Me; 10, R = Et). Molecular structures of 7 and 9 have been determined by single crystal X-ray diffraction studies. The structural characterization of 7 reveals a monomeric adduct between $Me_2(N_3)Ga$ with $NH_3$. The coordination geometry of the gallium atom of 7 is distorted tetrahedral. The general features of molecular geometry of 9 are similar to those of 7. The $^tBu$ and $N_3$ groups in 9 are trans to each other with respect to the dative Ga←N bond. Aluminum and gallium nitride (MN, M = Al, Ga) film growth has been carried out in a cold wall organometallic chemical vapor deposition (OMCVD) reactor. The crystalline structure, chemical composition, and optical property of the deposited films have been investigated by X-ray diffraction (XRD), pole figure analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and photoluminescence (PL). AlN thin films have been deposited by using single precursors 1 an...