Nagoya University · Physics and Astronomy
Professor Takeru Kumabe's research lab specializes in wide-bandgap semiconductor materials, particularly AlGaN/GaN heterostructures, with a focus on innovative doping techniques and device engineering for high-performance electronic and optoelectronic applications. The lab pioneers dopant-free approaches such as distributed polarization doping (DPD) to overcome limitations of conventional doping, enabling high hole mobility and superior carrier transport properties in p-type AlGaN layers. Key research directions include low-damage plasma etching processes, contamination-free heterojunction formation, and the development of high-efficiency HBTs and p-n diodes with ideal rectifying and electroluminescent behaviors. The lab emphasizes fundamental understanding of defect physics, carrier dynamics, and polarization effects in nitride semiconductors to advance next-generation power and high-frequency devices.
Figures are computed from collected data and may differ slightly.
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Abstract Inductively coupled plasma–reactive ion etching (ICP–RIE)-induced damage in heavily Mg-doped p-type GaN ([Mg] = 2 × 10 19 cm −3 ) was investigated by low-temperature photoluminescence (PL) and depth-resolved cathodoluminescence (CL) spectroscopy. From PL measurements, we found broad yellow luminescence (YL) with a maximum at around 2.2–2.3 eV, whose origin was considered to be isolated nitrogen vacancies ( V N ), only in etched samples. The depth-resolved CL spectroscopy revealed that t
Abstract An AlGaN/GaN heterojunction bipolar transistor (HBT) with N-p-n configuration was fabricated by the “regrowth-free” method, resulting in a contamination-free emitter-base AlGaN/GaN heterojunction. The low-bias-power-based low-damage inductively coupled plasma–reactive ion etching was employed in this study for emitter mesa definition instead of the conventional selective-area-regrowth technique. The method successfully minimized the etching-induced damage in the p-GaN base layer and the
Herein, the operation of dopant‐free GaN‐based p‐n junctions formed by distributed polarization doping (DPD) is experimentally demonstrated and their space charge profiles and carrier transport properties are investigated. The device exhibits ideal space charge profiles explained by polarization effects and demonstrates the excellent controllability of DPD. In addition, it shows rectification and electroluminescence under forward‐biased conditions. The carrier transport properties could be expla
We investigated the hole mobility limiting factors in dopant-free p-type distributed polarization-doped (DPD) AlGaN layers by an experimental method. p-DPD AlGaN exhibited a higher hole mobility than GaN:Mg with a similar room temperature hole concentration across all temperature ranges owing to the absence of ionized impurity scattering. In addition, unlike in n-DPD AlGaN, alloy scattering was not always critical in p-DPD AlGaN. The extracted alloy scattering potential was only 0.3 eV, which re
Minority carrier properties in dopant-free p-type distributed polarization doped (DPD) AlGaN layers were investigated on the basis of the forward-biased current density–voltage (J–V) characteristics of p–n+ diodes. The fabricated p-DPD AlGaN/n+–AlGaN:Si diodes exhibited ideal electrical characteristics despite the absence of acceptor atoms in the p-type layer. The extracted Shockley–Read–Hall lifetime exceeded 300 ps, which was longer than that reported for p-GaN:Mg on GaN substrates with a simi
Nearly ideal vertical AlGaN ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="0.7\ \leq x<1.0" display="inline"><m:mrow><m:mn>0</m:mn><m:mo>.</m:mo><m:mn>7</m:mn><m:mspace width="5.0pt" /><m:mo>≤</m:mo><m:mi>x</m:mi><m:mo><</m:mo><m:mn>1</m:mn><m:mo>.</m:mo><m:mn>0</m:mn></m:mrow></m:math> ) p-n diodes are fabricated on an AlN substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity d
Nearly ideal vertical AlxGa1-xN (\(0.7\ \le x<1.0\)) p-n diodes are fabricated on an AlN substrate. Distributed polarization doping (DPD) was employed for both p-type and n-type layers of the p-n junction, instead of conventional impurity doping, to overcome the major bottleneck of AlN-based material: the control of conductivity. Capacitance-voltage measurements revealed that the net charge concentration agreed well with the DPD charge concentration expected from the device layer structure. The
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