High temperature adduct formation of trimethylgallium and ammonia

Abstract

High temperature gas phase reactions between trimethylgallium ͑TMG͒ and ammonia were studied by means of in situ mass spectroscopy in an isothermal flow tube reactor. The temperature, pressure, and reaction time were chosen to emulate the gas phase environment typical of the metal-organic vapor phase epitaxy ͑MOVPE͒ of GaN. The main gas phase species is ͓(CH 3 ͒ 2 Ga:NH 2 ͔ x , where most probably xϭ3, resulting from the very fast adduct formation followed by elimination of methane. The further gas phase decomposition of this species proceeds through the stepwise elimination of methane. These studies indicate that little TMG exists within the growth ambient under most MOVPE growth conditions. The further gas phase reaction of ͓(CH 3 ͒ 2 Ga:NH 2 ͔ x may be responsible for the strong dependence of the MOVPE GaN growth rate and uniformity commonly observed. © 1996 American Institute of Physics. ͓S0003-6951͑96͒00527-X͔The metal-organic vapor phase epitaxy ͑MOVPE͒ has emerged as the current growth technique of choice for the growth of GaN for device structures.1 Recent successes in the MOVPE formation of commercially viable blue and green light emitters have resulted in an increased activity in understanding the growth process and its relationship to the physical properties of these materials. While MOVPE can produce these materials, the growth of device-quality GaN is complicated by the severe and complicated gas phase interactions, that occur between trimethylgallium ͓͑TMG or (CH 3 ͒ 3 Ga͔ and ammonia, NH 3 which are the commonly used growth precursors.2 These gas phase interactions have been suggested to lead to gas phase depletion of the growth nutrients leading to a degradation in the growth uniformity and efficiency.3 A primary gas phase reaction is the strong adduct forming reaction between NH 3 and TMG. [4][5][6][7] In this present study, we have directly monitored this gas phase reaction in order to better understand its impact on the growth process and system design under those conditions particularly important for MOVPE growth. The species responsible for growth are the direct result of these gas phase reactions.The gas phase reactions of both TMG and NH 3 , individually, are relatively understood at this point. The pyrolysis of TMG has been widely studied. [8][9][10][11][12] The initial step in the TMG decomposition is generally agreed to be the removal of the first methyl radical, resulting in methane as the main product released in the decomposition. In the stepwise first order decomposition of TMG, an apparent activation energy has been measured for the first and second methyl groups, of 58-60 kcal/mol ͑Refs. 8 and 10͒ and 35.4 kcal/ mol, respectively.8 Under similar thermal conditions ammonia is quite stable. The gas phase decomposition of NH 3 occurs only at very high temperatures. 13 The heterogeneous decomposition of NH 3 may, therefore, be essential to GaN growth.The gas phase reaction between (CH 3 ) 3 Ga and NH 3 is less understood, particularly at elevated temperatures characteristic of MOVPE ...

Computational fluid dynamics on gaseous and surface chemistry of GaN‐MOVPE system for various pressures

“…It is pointed out, however, that parasitic reactions are appeared in MOVPE-GaN growth. TMG and NH 3 form TMG:NH 3 under low pressure at temperature < 200 °C [9]. Fig.…”

Modeling of InGaN MOVPE in AIX 200 Reactor and AIX 2000 HT Planetary Reactor

“…The possibility of adduct formation due to pre-reaction between group-III metalorganic precursors and ammonia is discussed in several papers [15], [16]. This reaction leading to depletion of group-III precursors is generally assumed to be important during MOVPE of AlN and AlGaN but its relative contribution into the GaN and InGaN growth process is not clearly understood.…”

The GaN Growth by a Hot Filament Metalorganic Vapor Phase Deposition Technique

“…In order to suppress parasitic reactions and adduct formation [8], ammonia and TMG are introduced separately. The ammonia flow is introduced by the upper inlet while TMG, N 2 and H 2 were introduced from the bottom inlet.…”