Electrical characteristics of schottky barriers on 4H-SiC: The effects of barrier height nonuniformity

Abstract

Electrical properties, including current-voltage (I-V) and capacitance-voltage (C-V) characteristics, have been measured on a large number of Ti, Ni, and Ptbased Schottky barrier diodes on 4H-SiC epilayers. Various nonideal behaviors are frequently observed, including ideality factors greater than one, anomalously low I-V barrier heights, and excess leakage currents at low forward bias and in reverse bias. The nonidealities are highly nonuniform across individual wafers and from wafer to wafer. We find a pronounced linear correlation between I-V barrier height and ideality factor for each metal, while C-V barrier heights remain constant. Electron beam induced current (EBIC) imaging strongly suggests that the nonidealities result from localized low barrier height patches. These patches are related to discrete crystal defects, which become visible as recombination centers in the EBIC images. Alternative explanations involving generation-recombination current, uniform interfacial layers, and effects related to the periphery are ruled out.

Improved Schottky Contacts on n-Type 4H-SiC Using ZrB2 Deposited at High Temperatures

“…31,32 Our results indicate improved electrical characteristics and thermal stability of ZrB 2 /SiC Schottky contacts using high-temperature metal deposition, and this makes ZrB 2 a very attractive contact metallization for high-temperature applications.…”

A study of temperature-related non-linearity at the metal-silicon interface

“…Tung states 9 that at low temperature, Ohmic effects within the few conducting patches cause the dual current paths to become deconvoluted. This might explain the frequently cited and debated double bumps that can be seen variously in Si Schottky diodes 9,11 , SiC diodes [16][17][18][19][20] , GaAs diodes 23,24 , and also in heterojunctions 12,25 . The worsening of these effects in devices without guard rings or other edge protection, could futher be explained by low SBH patches at the device extremities which are not pinched off as well as those in the centre of the device, these being surrounded on all sides by the higher background patches [9][10][11] .…”

“…Other applications include carbon nanotube Schottky barrier transistors 6 , and Schottky solar cells, with materials including lead selenide nanocrystals 7 and graphene 8 . Despite over a hundred years of research and development into Schottky barriers, across all popular semiconductors and for the various applications, we still find ourselves with unanswered questions as to the nature of current flow across the barrier, especially in light of inhomogeneity at the metal-semiconductor interface 9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24] , which can result in multiple conduction paths through the non-uniform interface. Sources of interfacial inhomogeneity include processing remnants (dirt, contamination), surface roughness, native oxide, an uneven doping profile, crystal defects and grain boundaries 9,11,12 and it is generally now accepted that the surface is better represented as a random array of different patches, each of varying barrier height and area, as represented in the inset of Figure 1a.…”

“…Interfacial inhomogeneity has been cited 9-24 as the cause for many experimental results that deviate from this response. These so called non-linearities include high ideality factors 9,11,13 , the discrepancy between Schottky barrier heights (SBH) extracted via CV and IV techniques [9][10][11][12][13][14][15] , the "T 0 anomaly" 9,11,13 , double bumps within the semi-log turn-on characteristics 9,11,13,[16][17][18][19][20] , edge effects 9,11 and non-linearity within Richardson plots 22 . It was the papers written by Tung [9][10][11] however, that first introduced a model that adapted Equation 1 to fully explain the non-linearities in light of interfacial inhomogeneity and SBH fluctuation.…”

Nanoscale transport properties at silicon carbide interfaces

“…As an example, the occurrence of carrier transport mechanisms other than the thermionic emission, such as tunnelling current through the barrier [41] could be considered. However, at the typical doping levels used for n-type SiC Schottky diodes (<5×10 16 cm -3 ), the effect of tunnelling through the barrier at room temperature is very low under forward bias, and it may become significant only under strong reverse bias [42]. Hence, a common approach is to consider of a thin interfacial insulating layer, introduced to describe the presence of interface states at the metal/SiC contact [43].…”