GaN/SiC heterojunctions grown by LP-CVD

Heterojunction bipolar transistors (HJBT) on the basis of GaN/SiC heterostr uctures have several advantages over group III nitride heterostructures gro wn on sapphire. For example 6H-SiC has less of a thermal and structural mis match to GaN than sapphire has. Furthermore there is not the problem of opt ical recombination in a highly doped base region as there is for the group III nitrides on account of their direct bandgap. However, despite the well acknowledged potential of the GaN/SiC material sy stem there are still unanswered questions relating to the technology used a s well as to some fundamental properties of GaN/SiC heterostructures. There fore we investigated epitaxial growth and physical properties of n-GaN/p-Si C heterojunctions with respect to their significance to n-GaN/p-SiC/n-SiC H JBT. We grew n-type GaN (n = 10(18) cm(-3)) on p-type (p = 2 x 10(18) cm(-3)) an d n-type (II = 4 x 10(18) cm(-3)) 6H-SiC substrates in a horizontal hot wal l reactor. This approach is very similar to the more common HVPE. Instead o f synthesizing GaCl in situ from HCl and metallic Ga we used GaCl3 as the G a precursor. All our experiments were carried out at low pressures around I mbar resulting in a good homogeneity. As it is common for the more usual H VPE we grew GaN without a buffer layer. From thermal admittance spectroscopy (TAS) as well as temperature dependent I-V characteristics we gained knowledge about deep level defects and the r ole of interface traps. The microstructure of the interface was investigate d by transmission electron microscopy (TEM). Furthermore we present details about device processing by ion beam sputter etching with carbon dioxide (CO2) as the working gas. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.