Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates

The vertical bulk (drain-bulk) current (I-db) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental I-db (25-300 degrees C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (E-a), the (soft or destructive) vertical breakdown voltage (V-B), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (E-a = 0.35 eV at T = 25-300 degrees C; V-B = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E-a = 2.5 eV at T > 265 degrees C; V-B > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E-a = 0.35 eV at T > 150 degrees C; V-B = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored. (C) 2013 AIP Publishing LLC.