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

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...

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Bibliographic Details
Published inJapanese Journal of Applied Physics Vol. 52; no. 12; pp. 124102 - 124102-9
Main Authors Miyake, Hiroki, Amari, Koichi, Kimoto, Tsunenobu, Suda, Jun
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.12.2013
Subjects
Diodes
Doping
Electrical properties
Electroluminescence
Gain
Gallium nitrides
Heterojunctions
Semiconductor devices
Silicon carbide
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Summary: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 $1\times 10^{18}$ cm -3 instead of $1\times 10^{19}$ 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 $1\times 10^{18}$ cm -3 and 6H-SiC, whereas a current gain below $1\times 10^{-4}$ was obtained in the HBTs with a base doping concentration of $1\times 10^{19}$ cm -3 .
Bibliography:Structures of fabricated (a) heterojunction diodes and (b) HBTs. (Color online) Surface morphologies of (a) 6H-SiC on-axis substrate subjected to high-temperature gas etching before the GaN growth and (b) GaN grown on 6H-SiC on-axis surface. (Color online) Surface morphologies of (a) 4H-SiC 8° off-axis substrate subjected to high-temperature gas etching before the GaN growth, (b) GaN grown on 6H-SiC 3.5° off-axis surface, and (c) GaN grown on 4H-SiC 8° off-axis surface. Cross-sectional TEM image of GaN grown on 4H-SiC off-axis surface (zone axis). Dislocations generated at initial stage of growth vended toward step-bunched surface owing to the step-flow growth and were annihilated because of the step-bunching-induced annihilation. (Color online) PL spectra of GaN grown on 6H-SiC on-axis, 6H-SiC 3.5° off-axis, and 4H-SiC 8° off-axis substrates obtained at 4.2 K. (Color online) Temperature dependence of (a) carrier concentrations and (b) electron mobility of undoped- and Si-doped GaN grown on 6H-SiC 3.5° and 4H-SiC 8° off-axis substrates. Room-temperature $C$--$V$ characteristics of (a) n + -GaN/p-4H-SiC and (b) n + -GaN/p+-6H-SiC diodes ($N_{\text{d}} = 1\times 10^{19}$ cm -3 and $N_{\text{a}} = 1\times 10^{18}$ cm -3 ). Flat-band energy diagrams of (a) 4H-SiC/GaN and (b) 6H-SiC/GaN heterojunctions as calculated on the basis of the built-in voltages in $C$--$V$ measurements. $I$--$V$ characteristics of (a) n + -GaN/p + -4H-SiC and (b) n + -GaN/p + -6H-SiC heterojunction diodes ($N_{\text{d}} = 2\times 10^{19}$ cm -3 and $N_{\text{a}} = 1\times 10^{19}$ cm -3 ) measured at 200--500 K. $I$--$V$ characteristics of (a) n + -GaN/p-4H-SiC and (b) n + -GaN/p-6H-SiC heterojunction diodes ($N_{\text{d}} = 1\times 10^{19}$ cm -3 and $N_{\text{a}} = 1\times 10^{18}$ cm -3 ) measured at 200--500 K. (Color online) Schematic band diagrams of n + -GaN/p-SiC with (a) $N_{\text{a}} = 1\times 10^{19}$ cm -3 and (b) $N_{\text{a}} = 1\times 10^{18}$ cm -3 under reverse bias of 0.1 V. (Color online) Schematic band diagrams of n + -GaN/p-SiC with (a) $N_{\text{a}} = 1\times 10^{19}$ cm -3 and (b) $N_{\text{a}} = 1\times 10^{18}$ cm -3 under forward bias of 0.1 V. (Color online) (a) EL from n + -GaN/p-SiC heterojunction under forward bias. A dark-red EL was observed from n + -GaN/p-4H-SiC and n + -GaN/6H-SiC with $N_{\text{a}}\sim 1\times 10^{18}$ cm -3 . (b) PL spectra obtained in the same region. We observed a bright whitish-yellow luminescence from a GaN layer, whereas a dark-red luminescence was observed from p-4H-SiC and p-6H-SiC. (Color online) PL spectra of (a) n + -GaN, (b) p-4H-SiC, and (c) p-6H-SiC, showing whitish-yellow luminescence for n + -GaN and dark-red luminescence for p-SiC. Common-base $I_{\text{C}}$--$V_{\text{CB}}$ characteristics of (a) GaN/4H-SiC and (b) GaN/6H-SiC HBTs with base doping concentration of $5\times 10^{19}$ cm -3 . Common-base $I_{\text{C}}$--$V_{\text{CB}}$ characteristics of (a) GaN/4H-SiC HBTs and (b) GaN/6H-SiC HBTs with base doping concentration of $1\times 10^{18}$ cm -3 .
ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 23
ISSN:0021-4922
1347-4065
DOI:10.7567/JJAP.52.124102