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Scattering mechanism of electrons e.g. impurities, phonons etc. in solid-state materials influenced their electrical and optical properties. In order to achieve the best quality of AlGaN/GaN HEMT type heterostructures that will influence the HEMT transistor parameters it is essential to identify the scattering mechanism that appeared in epitaxial layers. Impurities such as hydrogen, carbon, Al, Ga, Si result from the applied reagent, construction of the reactor and MOVPE (Metalorganic Vapour Phase Epitaxy) process parameters. This mechanism will reflect on the values of Johnson, Key and Baliga figures of merit the knowledge of which is important to determine the application areas of materials. (carbon, oxygen, hydrogen).

Deep Level Transient Spectroscopy DLTS belong to capacitance transient thermal scanning method used for observing deep impurities and defect states in semiconductor [1]. Deep levels introduced near the middle of the energy gap by strong localized imperfections [2], are probably the main reason for impair the properties of High Electron Mobility Transistors (HEMT): gate-lag, drain-lag and virtual gate. DLTS method allows finding non-radiative recombination point defects in semiconductors, which could influence the carrier properties between the areas below the gate electrode and drain electrode. DLTS method gives the information about the energy level, concentration, thermal emission rate and the capture cross section of each trap. This technique cooperate quite well with luminescence, which allows observing shallow centers localized near the edge of valance or conduction band. In this paper will presented, the fundamental physical description of transition process in semiconductor, the basic results of DLTS measurements and the conclusions.

This article describes AlGaN/GaN type HEMT (High Electron Mobility Transistor) heterostructures, in which the second conducting channel exists, which exhibits unique dependence of both electron mobility and concentration on temperature. The transverse electric field associated with the classical Hall effect is the source of different electromotive forces in each layer. When a conductive path between 2DEG (two dimensional electron gas) and the GaN layer is created, the current between the layers starts to flow, changing the values of mobility and concentration acquired from Hall measurements. The classical Hall measurements in wide range of temperatures in AlGaN/GaN type HEMT heterostructures provide significant information about conductivity and the influence of the GaN layer.

In AlGaN/AlN/GaN heterostructures, as a result of spontaneous and piezoelectric polarization with the occurrence of donor surface states, a triangular potential well is formed on the interface, filled with two-dimensional electron gas with a concentration of 1013 cm􀀀2 and a mobility of 2000 cm2/(V s). An increase of the potential in the channel of an AlGaN/AlN/GaN high electron mobility transistor, caused by the flow of the drain current, results in: a decrease of the two-dimensional electron gas concentration, an increase of electric field and an increased drift velocity of electrons. At the drainage end of the gate, the electrons reach their maximum drift velocity which is correlated with the material limitations. Consequently, a rapid nonlinear increase of the channel potential, a decay of the twodimensional electron gas channel, and pushing of the electrons towards the buffer occurs. The vertical current component starts to increase then while the horizontal current component decreases. Moreover, between the gate and the drain electrodes the two-dimensional electron gas channel is gradually rebuilt due to the presence of a low electric field. The Advanced Physical Models of Semiconductor Devices software was used to simulate these phenomena in the structure of an AlGaN/AlN/GaN high electron mobility transistor.

The second conducting channel is created in AlGaN/GaN type high electron mobility transistor (HEMT) heterostructures deposited by the metal organic vapor phase epitaxy (MOVPE) technique, in which the pressure changes during the growth of the buffer GaN layer to ensure its high resistivity. It is stated that a second, parasitic, conducting channel is induced as a result of nonintentional doping that occurs at the GaN–GaN interface. The Hall measurements, in the wide range of temperatures, from 77 to 420 K, are used to obtain sheet resistivity, sheet carrier concentration, and electron mobility of the heterostructures. The theoretical model of the multilayer transport in AlGaN/GaN type HEMT heterostructures, based on an equivalent circuit, allows for estimation of compensatory current. Based on the theoretical model, the correction map for the Hall measurement of the samples with two conducting channels is evaluated. The measured electron mobility μmeas obtained from Hall measurement is applied for the determination of the 2D electron gas (2DEG) mobility μ1 of the samples with two conducing channels using the equation μ1¼ αμmeas. It is observed that the appropriate correction coefficient α depends on second channel parameters, i.e. the sheet resistance and mobility of the second conducting channel.