Alternative N precursors and Mg doped GaN grown by MOVPE

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Internet Journal o f

Nitride S emiconductor Research

Volume 1, Article 17

Alternative N precursors and Mg doped GaN grown by MOVPE B. Beaumont, M. Vaille, P. Lorenzini, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS T. Boufaden, B. el Jani Faculté des Sciences de Monastir, Tunisie. This article was received on June 3, 1996 and accepted on October 16, 1996.

Abstract In this paper, we address two different aspects relevant to the growth of GaN. The first part concerns alternative nitrogen source whereas in the second part, we report experimental results on Mg doping. Several nitrogen precursors have been used for the growth of GaN in MOVPE. To produce active species from N2 or NH3, a remote Plasma Enhanced Chemical Vapour Deposition (RPECVD) process has been implemented. In addition, nitrogen organic precursors, triethylamine and t-butylamine were also used. To accurately control the critical parameters of the MOVPE of GaN, we have implemented a laser reflectometry, which allows a real time in situ monitoring of the different steps of the growth. MeCp2Mg was used as Mg precursor for the p doping study. The dependence on the partial pressure of Mg precursor of dopant incorporation, electrical activity and growth rate are reported.

1. Introduction Because GaN single crystals of suitable size are not presently available, the epitaxy of GaN should be made on foreign substrates. Sapphire, 6H-SiC, MgAl2O4, GaAs and Si are commonly used, recently new substrates with closer lattice parameters have been reported, e.g. LiAlO2 and LiGaO2 [1]. In the present paper sapphire (0001) oriented substrates have proven to lead to high quality GaN epilayers. However, since the lattice mismatch between GaN and sapphire is 0.14, appropriate nucleation layers are of critical importance. Presently, NH3 is the most widely nitrogen precursor used for the growth of GaN but the requirement of high temperatures for the epitaxial growth leads to a high NH3 partial pressure to avoid nitrogen loss during the growth and very high V/III ratio are to be used. Other potential nitrogen source have been considered [2], but neither these nitrogen precursors, nor “ single source » adducts have produced high quality GaN yet.

2. Experimental GaN epilayers were grown in atmospheric growth chambers. In addition to the MO (TMGa, TMAl, MeCp2Mg), t-butylamine tBuNH2, triethylamine N(C2H5)3 and hydrides lines, the reactors are equipped with an in situ control of the growth by laser reflectometry and a microwave generator to produce plasma for the decomposition of NH3 or N 2. Beside NH3 standard pyrolysis, we used this plasma assistance and also the two organic nitrogen precursors mentioned above to grow epitaxial structures with the same design. Prior to the deposition of a 2-3 µm GaN layer at a temperature in the range 1000 to 1080°C, a 250 nm thick GaN buffer is first deposited at 600°C. The carrier gas is nitrogen except for the growth of GaN with t-butylamine where a mixture H2-N2 was tested. We have installed an i