Ballistic electron emission microscopy study of Schottky contacts on 6H- and 4H-SiC

Abstract

We have performed ballistic-electron emission microscopy (BEEM) on (Pd,Pt)/(6H,4H)-SiC(0001) Schottky contacts. Schottky barrier heights (SBHs) determined from the BEEM data using the Bell–Kaiser model are 1.27 eV/1.34 eV (Pd/Pt) for 6H- and 1.54 eV/1.58 eV for 4H-SiC. Our measurements also give the first direct evidence of a second conduction band minimum (CBM) on 4H-SiC about 0.14 eV above the overall CBM. Spatial inhomogeneity of SBHs were examined and shown to be no larger than the fitting error due to the system noise. Additionally, enhanced ballistic transmittance was observed over a region intentionally stressed by injecting high kinetic energy (10 eV above EF) hot electrons using BEEM in the Pt/4H-SiC sample.

Schottky barrier height measurements of Cu/Si(001), Ag/Si(001), and Au/Si(001) interfaces utilizing ballistic electron emission microscopy and ballistic hole emission microscopy

“…The SBHs for many metal/semiconductor systems have been extensively studied using BEEM and BHEM. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] With BEEM the tip can be positioned with a Electronic address: vlabella@albany.edu nanoscale resolution giving spatially resolved spectra and barrier heights, which has been performed for Au/GaAs(001) diodes where a Gaussian distribution of barrier heights was observed in support of interface dipole models. 27 The power law form of the Bell and Kaiser model is the standard method for extracting the Schottky barrier height from the BEEM spectra.…”

Valence band structure and band offset of 3C- and 4H-SiC studied by ballistic hole emission microscopy

“…2͑a͒ shows that a single threshold is quite sufficient for 3C-SiC. On n-type Schottky contacts it is well documented that a second BEEM threshold may indicate the existence of a second CBM at higher energy than the lowest CBM, [13][14][15][16][17] and by analogy a second BHEM threshold on p-type Schottky contacts suggests the presence of a second VBM at slightly lower energy than the highest VBM. We will return to this point later.…”

“…If the interface-state electric dipole is the same ͑for a given metal͒ on all polytypes, then the measured n-type SBH should indeed track the conduction band energy. These studies [13][14][15]17 also showed that BEEM could detect the presence and energy splitting of higher conduction bands in 4H-and 15R-SiC. This past work indicates that it should be possible to use SBH measurements on p-type SiC to measure the valence band offsets between SiC polytypes, and also to investigate the possible existence of a crystal-field split valence band in hexagonal SiC polytypes.…”

“…12 This should produce a small ͑Ͻ200 meV͒ crystal-field splitting in the valance band of the hexagonal polytypes that is absent in 3C-SiC. 3,6,7 It has been found [13][14][15] that differences in the n-type Schottky barrier heights ͑SBHs͒ measured using ballistic electron emission microscopy 16 ͑BEEM͒ on n-type 4H-, 6H-, and 15R-SiC closely track the corresponding difference in band gap. This suggests that measured differences in SBH can be used to track the corresponding bulk conduction band offsets.…”

Nanoscale transport properties at silicon carbide interfaces

“…Starting from the evidence that the I-V characteristics of macroscopic diodes show significant variations from device to device, although the interface is prepared under the same chemical conditions, Im et al [25,50] gave the first nanoscale approach to explain the non-ideal electrical behavior of Schottky contacts to SiC. In particular, they monitored the local fluctuations of the SBH in the Pd/6H-SiC system by means of Ballistic Electron Emission Microscopy (BEEM) [51], acquiring several BEEM spectra at different locations over the sample surface.…”