Investigation of n-GaN/p-SiC/n-SiC heterostructures

GaN/SiC heterojunction bipolar transistors (HBTs) with an ultrathin AlN spacer layer at the n-GaN/p-SiC emitter junction are proposed for the control of the electronic properties of GaN/SiC heterojunctions. The insertion of an AlN spacer is found to be promising in terms of improving electron injection efficiency owing to the reduced potential barrier (0.54 eV) to electron injection and reduced recombination via interface traps. We also investigated the effect of pre-irradiation of active nitrogen atoms (N*) prior to AlN growth for the control of the electronic properties of GaN/AlN/SiC heterojunctions. We found that the potential barrier was further reduced to 0.46 eV by N* pre-irradiation. The HBT structure was successfully fabricated using our newly developed process featuring ion implantation and Pd ohmic contacts to obtain a low contact resistivity to a p-SiC base at a temperature as low as 600 °C. A fabricated HBT without an AlN layer showed a low current gain (α ∼ 0.001), whereas the GaN/AlN/SiC HBT showed improved current gains of 0.1 in the case of using a 1-nm-thick AlN spacer without N* pre-irradiation and 0.2 in the case of using a 2-nm-thick AlN spacer with N* pre-irradiation.

Section: Introductionmentioning

confidence: 99%

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

Kimoto

Suda

2014

“…The fabrication of GaN/SiC HBTs was first reported by Pankove et al 7) followed by several other groups. 8,9) However, none of these HBTs offered common-emittermode operation owing to the large leakage at the emitter junction; thus, research focused on n-GaN/p-SiC emitter junctions is necessary to achieve common-emitter-mode operation in the HBTs.…”

Section: Introductionmentioning

confidence: 99%

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

Amari¹,

Kimoto²,

Suda³

2013

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.

“…Heterojunction bipolar transistors (HBTs) are theoretically expected to have a much higher current gain than conventional BJTs because their wide-bandgap emitter can suppress the injection of holes from the base to the emitter. The fabrication of GaN/SiC HBTs was first reported by Pankove et al 9) and then by Lebedev et al 10) However, no HBTs have shown common-emitter mode operation owing to the large leakage at their base-emitter junction. To improve the characteristics of GaN/SiC HBTs, AlGaN/SiC heterojunctions have been investigated by Danielsson et al 11) However, the band offsets between AlGaN and SiC could not be controlled by adjusting Al composition.…”

Section: Introductionmentioning

confidence: 99%

Current Transport Characteristics of Quasi-Al_xGa_1-xN/SiC Heterojunction Bipolar Transistors with Various Band Discontinuities

Okuda

Kimoto

Suda

2012

The current transport characteristics of quasi-Al x Ga1-x N/SiC heterojunction bipolar transistors (HBTs) with various band discontinuities were investigated in a low-current range using a Gummel plot. In the low-current range, the base currents of the HBTs were dominated by recombination currents. The collector current characteristics of the HBTs in the low-current range were almost the same in spite of the various band discontinuities, and the ideality factor n was 1.0. The band discontinuities at the heterojunction had no effect on electron injection in the low-current range. This is because the collector currents were dominated by diffusion process in the base region rather than by injection process at the AlGaN/SiC interface.