Fabrication and characterization of heterojunction diodes with HVPE-grown GaN on 4H-SiC

Characterization of heterojunction diodes with hydride vapor phase epitaxy grown AlGaN on 4H–SiC

“…The GaN and the reference sample showed nice linearity and an ideality factor with a small temperature dependence. The built-in potential for the GaN sample agrees well with the previously reported value, 13 and also agrees well with the extracted value from C -V measurements discussed below in Sec. III B.…”

“…Several studies on heterodiodes have been previously published. [7][8][9][10][11][12][13] Common to all reported diodes was the fact that the measured current increased above the noise level at a forward bias of approximately 1 V. This low turn-on voltage was located approximately 1 V lower than what was expected from simulations using standard drift-diffusion theory. A proposed mechanism for this has been a high recombination rate at the interface, assisted by tunneling through the barrier created by the depletion region.…”

“…32 This second order technique resulted in an extracted built-in potential for the GaN sample that agreed well with the previously reported GaN/4H-SiC diode fabricated with the same process. 13 Furthermore, the nonlinearity was also similar for all the AlGaN samples and the GaN sample, which were fabricated from the same wafer. To further verify the nonlinear extraction, a Ti Schottky contact was fabricated directly on the surface of the p-type epilayer as described in Sec.…”

“…13 The proposed tunneling assisted recombination discussed previously can be due to a combination of the lattice mismatch and the GaN/SiC heterojunction band alignment, where E C (GaN)ϽE C (4H-SiC) or of type II. 9,10,12,13,15 This band alignment type produces higher carrier concentrations close to the interface at forward bias, and the lattice mismatch can introduce high concentrations of recombination centers.…”

“…13 The proposed tunneling assisted recombination discussed previously can be due to a combination of the lattice mismatch and the GaN/SiC heterojunction band alignment, where E C (GaN)ϽE C (4H-SiC) or of type II. 9,10,12,13,15 This band alignment type produces higher carrier concentrations close to the interface at forward bias, and the lattice mismatch can introduce high concentrations of recombination centers. The band alignment of AlN has E C (AlN)ϾE C (4H-SiC) 16 and, as mentioned previously, the lattice match for AlN is only 1%, so these properties should gradually improve with increasing Al composition for Al x Ga 1Ϫx N ͑see the band diagram in Fig.…”