Poole Frenkel Effect on the DX Centers in III-V Ternary Alloys
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POOLE FRENKEL EFFECT ON THE DX CENTERS IN Il-V TERNARY ALLOYS H. ALTELARREA, J. BOSCH, A. PEREZ, J. SAMITIER AND J.R. MORANTE. Catedra d'Electrbnica. Fac.Ffsica. Universitat de Barcelona. Diagonal 645-647. Barcelona 08028. Spain.
ABSTRACT The dependence of the DX centers thermal emission rates on the electric field has been measured by Isothermal Transient Spectroscopy (ITS) and differential ITS (DITS) techniques. These techniques allow us to achieve a more accurate analysis of these defects than the DLTS. which ability for the study of DX centers is discussed. This dependence has been found to be mainly due to a Poole-Frenkel effect and is the cause of the non-exponentiality of the thermal emission transients.
INTRODUCTION In the last years there have been a lot of papers devoted to the DX centers in III-V ternary alloys, due to the detrimental influence of these traps on the performance of high electron mobility transistor (HEMT) devices. In these papers different techniques have been used to report values of parameters of great interest in order to explain the microscopic nature of donors with a DX type behaviour. However, their physical nature is still subject of controversy and the deduction of the parameters can depend on the physical model choosen, as for example the parameters related to the thermal emission and capture kinetics. In this framework, the discussion reported by Lang et al. in early papers [1] shows that the application of the deep level transient spectroscopy (DLTS) for the characterization of these centers is not advisable. However, this technique has been extensively used and different authors have invoked several models, such as the broadening [2], local environment changes [3] and cross section distribution [4]. to explain the DLTS spectra. Generally, a comparative study between these models and experimental single shot transients at different bias and temperatures has not been made. These models are not the only physical mechanisms which can explain the non exponential behaviour of the thermal emission and capture kinetics. So, the influence of the electric field on the microscopic parameters associated to the DX center has been reported [5] and even though the data from Calleja et al. [6] of the non-exponentiality factor do not show any dependence on the electric field, their experiments always correspond to transients carried out near edge region and, hence, at low field conditions. We have to remark that, taking into account the characteristics of these centers, the DLTS spectra are obtained without complete filling of the centers. Bearing this in mind, this work has a double aim: i) to show that the use of the DLTS with non-saturated trap filling of the centers is not suitable, and ii) to characterize the center using other technique based on the time resolved analysis of the Isothermal Transients (ITS) and their differences (DITS). This characterization allows us to measure the dependence on the electric field of the DX emission kinetics.
EXPERIMENTAL DETAILS For an ideal level wi
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