Influence of growth process scheme on the properties of AlGaN/AlN/GaN heterostructures

To check the influence of different process parameters, such as precursors (TMAl and TMGa) flow rates, growth interrupt time between subsequent stages of the growth for purging the reactor, on the properties of the two dimensional electron gas (2DEG) in the AlGaN/AlN/GaN heterostructure, seven sets of HEMT structures were developed and investigated. It was demonstrated that for the growth of canonically the same "sandwich" structure, several growth process schemes can be applied, and different properties of fabricated AlGaN/AlN/GaN can be obtained. It was shown, that changing Al content in the AlGaN barrier layer by modifying TMAl flow rate results in significant decrease in 2DEG mobility compared to the method in which TMGa flow rate is adjusted to keep the assumed composition. The presented results also showed, that the growth interruption between successive stages of AlGaN/AlN/GaN growth has a distinct impact on the mobility and concentration of 2DEG in HEMT's. The transport properties of the fabricated heterostructures were studied by impedance spectroscopy technique. Specific parameters of growth process, such as growth rate and Al content, were obtained by in-situ interferometry and photoluminescence technique. There are many publications which describes the influence of different structure parameters, e. g. composition of the AlGaN barrier layer, thickness of the AlN interlayer, however the information is rather fragmentary and it is difficult to compare quantitative results deriving from various groups. The purpose of this article was to show the key HEMT's structure parameters in relation to MOVPE process scheme, influencing the electrical transport of 2DEG. Detailed explanation of physical phenomenas was not the main aim of this work and will be presented later. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim