Growth, Electrical Characterization, and Electroluminescence of GaN/SiC Heterojunction Diodes and Bipolar Transistors Fabricated on SiC Off-Axis Substrates

Abstract

The growth, electrical characterization, and electroluminescence (EL) of GaN/SiC heterojunction bipolar transistors (HBTs) are presented. GaN grown on off-axis SiC by molecular beam epitaxy showed step bunching owing to the large off-angle of SiC substrates, which contributed to the annihilation of edge dislocations. We investigated the impact of base doping concentration and SiC polytype (4H and 6H) on the characteristics of GaN/SiC heterojunction diodes. By utilizing a reduced doping concentration of 1×1018 cm-3 instead of 1×1019 cm-3, we suppressed the tunneling current via interface traps, resulting in an improved rectifying behavior in the diodes. Capacitance–voltage (C–V) and EL characteristics revealed that the band lineup of GaN/SiC is of type II, and 6H-SiC is better for electron injection. In accordance with diode characteristics, the fabricated GaN/SiC HBTs showed an improved common-base current gain of 0.03 by employing a reduced base doping concentration of 1×1018 cm-3 and 6H-SiC, whereas a current gain below 1×10-4 was obtained in the HBTs with a base doping concentration of 1×1019 cm-3.

Effect of ultrathin AlN spacer on electronic properties of GaN/SiC heterojunction bipolar transistors

“…Note that With N* pre-irradiation GaN/SiC HBTs previously reported showed significant leakage in both emitter-base and collector-base diodes owing to high-temperature metallization annealing at 900 °C. 14) The suppression of the leakage is attributed to our newly developed process featuring ion implantation and Pd ohmic contacts to obtain low resistivity to the p-SiC base at a temperature as low as 600 °C, as discussed above.…”

“…Note that the conduction band offset of 0.74 eV is almost the same as that of a previously reported value. 14) By utilizing an AlN spacer, the height of the barrier to electrons has been reduced from 0.74 to 0.54 eV, indicating that the GaN/AlN/SiC heterojunction may have better electron injection efficiency than the GaN/SiC heterojunction. Note that the AlN layer is so thin that electrons can pass through via tunneling.…”

“…[9][10][11][12][13] We previously studied GaN/SiC HBTs and suppressed the reverse leakage as well as recombination current at an n-GaN/p-SiC heterojunction by reducing the base doping concentration from 1 © 10 19 to 1 © 10 18 cm ¹3 . 14) Although common-base characteristics were obtained, the current gain was still very low (¡ ³ 0.01). Since the low current gain must be attributed to low emitter injection efficiency, it is very important to control the electronic properties of the n-GaN/ p-SiC emitter junction.…”

Investigation of Nucleation and Intermixing at Hetero-Interface in III-Nitride-4H-SiC Structures

“…III-Nitride/SiC heterostructure devices are a promising approach for improving the performance of SiC devices such as bipolar transistors and avalanche photodiodes [1][2][3][4]. GaN/SiC heterojunction bi-polar junction transistors (HBT) can take advantage of the wider bandgap GaN base region to improve the current gain over SiC HBTs [2].…”

“…III-Nitride/SiC heterostructure devices are a promising approach for improving the performance of SiC devices such as bipolar transistors and avalanche photodiodes [1][2][3][4]. GaN/SiC heterojunction bi-polar junction transistors (HBT) can take advantage of the wider bandgap GaN base region to improve the current gain over SiC HBTs [2]. III-Nitride/SiC heterostructure avalanche photodiodes (APDs) are an exciting approach for extending the performance of 4H-SiC throughout the ultraviolet spectrum by either improving the absorption of near ultraviolet photons or mitigating the loss of carriers generated by deep ultraviolet photons to surface recombination over homogenous SiC APDs [3][4].…”