Self heating in AlInN/AlN/GaN high power devices: Origin and impact on contact breakdown and IV characteristics

It is observed experimentally that high electron mobility transistor devices with short channel length processed from nitride AlInN/AlN/GaN heterostructures containing 2D electron gases (2DEGs) with densities beyond 2 x 10(13) cm(-2) exhibit temperatures up to 1000 K if they are driven at high drain-source voltages. Corresponding current-voltage (IV) characteristics show a peaklike behavior with a maximum saturation current (I-DS,I-max) up to 2 A/mm. The goal of this article is to describe device heating in the framework of LO phonon statistics and its dependence on channel length, carrier density, and applied voltage. The strong channel heating, on the other hand, affects the transport mobility and must be taken into account to correctly interpret IV characteristics and resolve the discrepancy with metal oxide semiconductor field effect transistor models. Furthermore, the breakdown of ohmic contacts can directly be related to the channel temperature, i.e., the channel reaches the melting point of the contact metallization. In addition, the model correctly predicts the behavior of IV curves versus 2DEG density and transistor initial ambient temperature. For 2DEGs confined in triangular potential wells formed at the heterointerface, a maximum IDS is found for 2DEG densities between 2 x 10(13) and 3 x 10(13) cm(-2). (C) 2011 American Institute of Physics. [doi: 10.1063/1.3552932]

Temperature mapping of Al0.85In0.15N/AlN/GaN high electron mobility transistors through micro-photoluminescence studies

Jean-François Carlin, Eric Feltin, Marcus Gonschorek, Nicolas Grandjean, Marcel Py, Dobri Simeonov

Crack-free lattice-matched Al0.85In0.15N/GaN heterostructures were grown on sapphire substrates with barrier thicknesses up to 100 nm which exhibit very high polarization-induced electron sheet density (>2.5 x 10(13) cm(-2)) located at the heterointerface. These layers have been further processed as high electron mobility transistors (HEMTs). Optical characterization of these structures was carried out by photoluminescence and microphotoluminescence (mu PL) for different biased voltages. The insertion of an InGaN back-barrier unambiguously reveals that spatially direct optical recombinations occur within the AlInN alloy. Since the GaN excitonic bandgap is very sensitive to local temperature changes, the mu PL technique allows mapping very precisely the actual local temperature distribution in biased HEMT devices. For a gate length of 1.5 mu m temperatures up to 1130 K were found at a drain-source voltage of 20 V thus indicating the presence of a hot phonon bath.

2009

Physical Properties of Al1-xInxN/(AIN)/GaN (0.07

Marcus Gonschorek

AlInN is a material which is known to be difficult to be grown among the III-nitride ternary compounds. It attracted much attention only recently and starts to be studied intensively mainly for electronic applications. The aim of this work is manifold. Various structural, electrical and optical measurements are brought together to underline the outstanding quality of AlInN epi-layers grown by metalorganic vapor phase epitaxy (MOVPE). Especially the electrons confined at the heterointerface of coherently grown AlInN on GaN buffer layers determine crucially the electronic properties. An appropriate model based on charge balance is proposed allowing the extraction of all significant electrical properties. An AlN interlayer has been introduced at the AlInN/GaN interface and was found to tremendously affect transport properties. This issue is studied intensively and results indicate that even slightest deviations from atomically perfect interfaces leads to the creation of huge piezoelectric fields disturbing carrier transport in the case of strongly mismatched epilayers. A similar debate was conducted concerning the localization of carriers in InGaN quantum wells. High electron mobility transistors (HEMT) processed from these heterostructures exhibits excellent device performance exceeding 2 A/mm even on sapphire substrates. This are the highest currents ever reported for nitride heterostructures. The same structures grown on Si(111) substrates allow reaching cut-off frequency in excess of 100 GHz . However, results are puzzling and on at first sight striking since the device saturation currents of structures grown on SiC are similar to results on sapphire despite its much larger thermal diffusivity. Therefore we studied the temperature arising in the device under applied voltages using a micro-photoluminescence (µPL) setup. To our knowledge this is the first study of this type. The main advantage is the use of the short wavelength for excitation in comparison with well-established Raman methods. However we find from this analysis a significant heat development up to 1200 K for devices with 5 µm drain-source distance. The heating can be understood in terms of excited optical phonons due to field accelerated electrons under applied voltages. The comparison of the available amount of phonons in the finite volume covered by the 2D electrons and the number of created phonons in the acceleration process allows formulating a simple relation for the saturation currents as a function of the transport properties. However, this mechanism also explains why the saturation currents are far below expected values from simple velocity saturated currents models and independent of the substrate. However, heat, i.e. the decomposition of local optical phonons into acoustical phonons with large group velocity, is dissipated differently depending on substrate influencing therefore mainly the reliability of the devices. Beside the electrical breakdown due to avalanche carriers a second thermally induced breakdown mechanisms is proposed. Finally, the capability of those heterostructures for sensing is discussed. Especially the electrically response on external stimulus such as UV radiation and the exposition of the surface to polar liquids is investigated.

EPFL2011

Temperature mapping of Al0.85In0.15/AlN/Gan high electron mobility transistors through micro-photoluminescence studies

Jean-François Carlin, Eric Feltin, Marcus Gonschorek, Nicolas Grandjean, Marcel Py, Dobri Simeonov

EDP Sciences2009

Physical Properties of Al1-xInxN/(AIN)/GaN (0.07

Marcus Gonschorek

EPFL2011