Influence of Overheating Effect on Transport Properties of AlGaN/GaN Heterostructures
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Influence of Overheating Effect on Transport Properties of AlGaN/GaN Heterostructures Andriy Kurakin1, Svetlana Vitusevich1, Mykhailo Petrychuk2, Hilde Hardtdegen1, Serhiy Danylyuk1, Alexander Belyaev3, and Norbert Klein1 1 Institute of Bio- and Nanosystems, Forschungszentrum Juelich, Juelich, 52425, Germany 2 National Taras Shevchenko University of Kyiv, Kyiv, 01033, Ukraine 3 V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, 03028, Ukraine
ABSTRACT We report on peculiarities observed in electrical characteristics of AlGaN/GaN transmission line model (TLM) devices. Special attention is given to self-heating processes and thermal effects in AlXGa1-XN/ GaN based devices. The set of the samples under test contains conventional Al33Ga67N/GaN heterostructure with 1 µm thick buffer on a sapphire substrate and wafers which differ from the conventional one by a layer (SiC substrate, additional AlN spacer, Al mole fraction of the barrier). The Al30Ga70N/GaN structures with 3 µm buffer grown on thin (450µm) and thick (3 mm) sapphire substrate investigated as well. Comprehensive analysis of the experimental data (current-voltage characteristics, noise figures) combined with the simulation of the thermal budget of the devices reveals strong dependence of device performance and overheating not only on substrate type but also on buffer thickness as well as Al mole fraction of barrier layer. Regarding this the optimal conditions for observation of hot-electron effects can be determined. The obtained results can be used as guidelines in optimization of wafer and device design in order to reach the best performance frequently predicted for nitride based structures. INTRODUCTION AlGaN/GaN heterostructures can operate at very high power in dc and rf regimes due to superior properties of III-nitride materials. At the same time, a higher level of dissipated power causes the higher overheating in the structures. Considering the fact that the temperature is the driving force for aging processes in devices, it is obvious that the investigations of the thermal effects in 2DEG of GaN-based heterostructures are of great importance. Additionally, such studies result in better understanding of the transport properties which affect device performance, and allow us to determine the conditions under which hot-electron effects play the dominant role in electron transport. Usually, sublinear behavior of current in static current-voltage (I-V) characteristics of TLM, drain current reduction of HEMT at high biases are associated with self-heating processes as well as hot-electrons effects [1]. Recently Kuzmik at al. [2] have noticed that sublinearities in I-V behavior of TLM devices at high biases are observed even in nanosecond pulse regime, and the depletion of the channel as a result of surface traps charging, is only responsible for the nonlinear behavior of I-Vs. It is quite possible that suggested mechanism dominates after the
elimination of the overheating due to very short pulse d
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