Electrical Properties of Quantum Wells in III-NITRIDE Alloys and the Role of Defects
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Electrical Properties of Quantum Wells in III-NITRIDE Alloys and the Role of Defects Daniela Cavalcoli, Albert Minj, Saurabh Pandey, Beatrice Fraboni and Anna Cavallini Physics and Astronomy Department, University of Bologna, Viale C Berti Pichat 6/II, I40127 Bologna, Italy ABSTRACT III-nitrides (III-Ns) semiconductors and their alloys have shown in the last few years high potential for interesting applications in photonics and electronics. III-Ns based heterostructures (HS) have been under wide investigation for different applications such as high frequency transistors, ultraviolet photodetector, light emitters etc. In the present contribution a III-Ns based heterostructure, in particular the nearly lattice matched Al1xInxN/AlN/GaN HS will be discussed. The formation of the two dimensional electron gas (2DEG), its origin, its electrical and optical properties, the confined subband states in the well and its effect on the conduction mechanisms have been studied. Moreover, extended defects and their effect on the degradation phenomena of the 2DEG have been analyzed. INTRODUCTION Notwithstanding the wide application range and interest in III-Nitride based heterostructures (HS), many material-related fundamental issues of these materials are still under investigation: interdiffusion of mobile species, In or Al incorporation or segregation [1,2] and the role of extended defects on the electrical properties [3-6] are still debated. As a case study of such heterostructures, the nearly lattice matched Al1-xInxN/AlN/GaN system will be here analyzed. This system has been studied only quite recently, as before 2005 very few data were available on these alloys, and high electron mobilities transistor were basically developed on AlGaN/GaN HS [7]. Later on, it was found that lattice-matched AlInN/GaN heterostructures exhibit more than twice the amount of electrons confined at the AlGaN/GaN heterointerface, and hence a serious interest arose in those HS for applications in high power electronics. In Al1-xInxN/GaN HS, the strong band gap difference between AlN and Al1-xInxN (with low In content, x around 0.13-0.14) and the very high polarization- induced electric field create a triangular potential well at the heterointerface, which is able to confine electrons, thus a two dimensional electron gas (2DEG) forms in the well. The electrons forming the 2DEG may suffer from poor in-plane transport properties due to alloy disorder induced scattering. To overcome this difficulty, the insertion of an AlN interlayer, an approach already explored within the AlGaN/GaN system, has been used. This helps to keep the electrons better confined in the GaN channel and prevents 2DEG electrons from alloy scattering. High carrier density (around 2×1013cm-2) and high mobility (around 2×103 cm2/Vs) [7] are usually obtained in these structures. An example of such a well is sketched in fig1. Notwithstanding the quite good structural and electrical properties of these structures, we have to remind here that III-Ns and their alloys suffer for the absence of
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