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This work reports on the effect of high temperature annealing on the electrical properties of p-type implanted 4H-SiC. Ion implantations of Aluminium (Al) at different energies (30 -200 keV) were carried out to achieve 300 nm thick acceptor box profiles with a concentration of about 10 20 at/cm 3 . The implanted samples were annealed at high temperatures (1675-1825 °C). Morphological analyses of the annealed samples revealed only a slight increase of the surface roughness RMS up to 1775°C, while this increase becomes more significant at 1825°C (RMS=1.2nm). Room temperature Hall measurements resulted in a hole concentration in the range 0.65-1.34×10 18 /cm 3 and mobility values in the order of 21-27 cm 2 V -1 s -1 . The temperature dependent electrical measurements allowed to estimate an activation energy of the Al-implanted specie of about 110 meV (for the post-implantation annealing at 1675°C) and a fraction of active p-type Al-dopant ranging between 39% and 56%. The results give useful indications for the fabrication of 4H-SiC JBS and MOSFETs.The main dopant species for SiC are Nitrogen (N) and Phosphorous (P) for n-type doping, and Aluminum (Al) for p-type doping. High post-implantation annealing temperatures (> 1500°C) are typically required to bring these species in substitutional positions and achieve their electrical activation [5,6,7]. In particular, selectively doped p-type regions are key parts of both JBS and MOSFETs and the control of their electrical properties has a significant impact on several devices parameters (e.g., Ohmic contacts formation, device on-resistance, threshold voltage and channel mobility, etc.).Hence, understanding the dependence of the properties of p-type implanted layers on the activation annealing temperature is very important for device manufacturers to set the right process for the optimal device characteristics. In this context, although several investigations reported on the properties of Al-implanted 4H-SiC layers [8,9,10], the large variety of experimental conditions and the evolution of the annealing procedures always make this topic open to scientific discussions.Hall-effect measurements are often used to study the electrical properties of p-type 4H-SiC layers, in order to determine key parameters like the holes concentration and mobility [11]. A critical issue of this methodology is the choice of the Hall scattering factor rH for SiC [12,13]. In fact, the difficulty to extract the mobility and the free hole concentration from Hall measurements is related to the correct knowledge of rH. However, many authors often interpret the experimental Hall results on p-type 4H-SiC assuming rH=1, which in turn leads to an overestimation of the doping level in the material [9,14]. Only few works specifically reported experimental calculations of the Hall scattering factor rH for SiC [15,16], whose findings should be considered for a correct analysis of the currently available data.This paper reports on the morphological and electrical properties of p-type implanted 4H-SiC annealed...

This paper is a report on Ohmic contacts on n-type and p-type type cubic silicon carbide (3C-SiC) layers grown on silicon substrates. In particular, the morphological, electrical and structural properties of annealed Ni and Ti/Al/Ni contacts has been studied employing several characterization techniques. Ni films annealed at 950°C form Ohmic contacts on moderately n-type doped 3C-SiC (ND ~ 1×10 17 cm -3 ), with a specific contact resistance of 3.7×10 -3 Ωcm 2 . The main phase formed upon annealing in this contact was nickel silicide (Ni2Si), with randomly dispersed carbon in the reacted layer. In the case of a p-type 3C-SiC with a high doping level (NA ~ 5×10 19 cm -3 ), Ti/Al/Ni contacts were preferable to Ni ones, as they gave much lower values of the specific contact resistance (1.8 ×10 -5 Ωcm 2 ). Here, an Al3Ni2 layer was formed in the uppermost part of the contact, while TiC was detected at the interface. For this system, a temperature dependent electrical characterization allowed to establish that the thermionic field emission rules the current transport at the interface. All these results can be useful for the further development of a devices technology based on the 3C-SiC polytype.

This Letter reports on the active dopant profiling and Ohmic contact behavior in degenerate P-implanted silicon carbide (4H-SiC) layers. Hall measurements showed a nearly temperature-independent electron density, corresponding to an electrical activation of about 80% of the total implanted dose. Using the Hall result as calibration, the depth resolved active P-profile was extracted by scanning capacitance microscopy (SCM). Such information on the active P-profile permitted to elucidate the current injection mechanism at the interface of annealed Ni Ohmic contacts with the degenerate n-type 4H-SiC layer. Modeling the temperature dependence of the specific contact resistance with the thermionic field emission mechanism allowed extracting a doping concentration of 8.5 × 1019 cm−3 below the metal/4H-SiC interface, in excellent agreement with the value independently obtained by the SCM depth profiling. The demonstrated active dopant profiling methodology can have important implications in the 4H-SiC device technology.

The electrical behavior of Ni Schottky barrier formed onto heavily doped (ND>10 19 cm -3 ) n-type phosphorous implanted silicon carbide (4H-SiC) was investigated, with a focus on the current transport mechanisms in both forward and reverse bias. The forward current-voltage characterization of Schottky diodes showed a reduced barrier height (B=0.94 eV), with the current transport dominated by a thermionic-field emission mechanism. On the other hand, the reverse bias characteristics could not be described by a unique mechanism. In fact, under moderate reverse bias, implantation-induced damage is responsible for the temperature increase of the leakage current, while a pure field emission mechanism is approached with bias increasing. A numerical study of the potential distribution in a junction barrier Schottky (JBS) diode structure allowed demonstrating that metal/4H-SiC barriers on such heavily doped layers can find interesting applications in real devices.

This paper reports on the electrical activation and Ohmic contact properties on p-type Al-implanted silicon carbide (4H-SiC). In particular, the contacts were formed on 4H-SiC-implanted layers, subjected to three different post-implantation annealing processes, at 1675 °C, 1175 °C, and 1825 °C. Under these post-implantation annealing conditions, the electrical activation of the Al dopant species increased from 39% to 56%. The Ti/Al/Ni contacts showed an Ohmic behavior after annealing at 950 °C. The specific contact resistance ρc could be lowered by a factor of 2.6 with the increase of the post-implantation annealing temperature. The result can be useful for application in device fabrication. Moreover, the dependence of ρc on the active acceptor concentration followed the thermionic field emission model, with a barrier height of 0.63 eV.

In this paper, the forward and reverse current transport mechanisms in as-deposited and 400 °C annealed tungsten carbide (WC) Schottky contacts on AlGaN/GaN heterostructures have been studied. In particular, under forward bias, the WC/AlGaN Schottky contacts exhibited a deviation from the ideal thermionic emission model due to the occurrence of a tunneling component of the current. From the temperature dependence of the ideality factor, a characteristic tunneling energy E00 in the range of 33–36 meV has been estimated. On the other hand, two different transport mechanisms have been identified under reverse bias. At low reverse bias (VR < 2 V), Poole–Frenkel emission rules the current transport, with an emission barrier ϕt = 0.68 eV in the as-deposited contact, which increases up to ϕt = 0.79 eV upon annealing at 400 °C. This behavior has been correlated with the improvement of the metal/AlGaN electronic properties. At higher reverse bias (VR > 2 V), the leakage current is dominated by a thermally activated process with an activation energy (0.27 eV) that is independent of the Schottky contact fabrication process. In this case, the temperature dependence of the leakage could be well described by a two-dimensional variable range hopping conduction associated with the presence of surface defects in the material.

This paper compares the metal/semiconductor barrier height properties of non-recessed Ti/Al/Ti and Ta/Al/Ta contacts on AlGaN/GaN heterostructures. Both contacts exhibited a rectifying behavior after deposition and after annealing at temperatures up to 550 °C. The ohmic behavior was reached after annealing at 600 °C. High-resolution morphological and electrical mapping by conductive atomic force microscopy showed a flat surface for both contacts, with the presence of isolated hillocks, which had no significant impact on the contact resistance. Structural analyses indicated the formation of the Al3Ti and Al3Ta phases upon annealing. Furthermore, a thin interfacial TiN layer was observed in the Ti/Al/Ti samples, which is likely responsible for a lower barrier and a better specific contact resistance (c = 1.6 10−4 Ωcm2) with respect to the Ta/Al/Ta samples (c = 4.0 10−4 Ωcm2). The temperature dependence of the specific contact resistance was described by a thermionic field emission mechanism, determining barrier height values in the range of 0.58–0.63 eV. These results were discussed in terms of the different microstructures of the interfaces in the two systems.