Batch Furnace Chemical Vapor Deposition of Pure Boron Layers on Si and GaN Substrates for Low-Leakage-Current Diode Fabrication

Abstract

Boron deposition on both n-Si and n-GaN in the temperature range 250 - 500 °C, has been shown to form diodes with low saturation currents, i.e., electron injection from the n-substrate into the B-layer was efficiently suppressed. Moreover, down to 3-nm-thick B-layers on Si were shown to form a material barrier to Al, opening the possibility of fabricating Au-free gates for gallium-nitride high-electron-mobility transistors (GaN HEMTs). Several different chemical- and physical-vapor deposition (CVD/PVD) methods for depositing B have been studied for fabricating p+n-like Si diodes, called PureB diodes, all with comparable results. In this paper, the deposition of B-layers from diborane in a CVD batch furnace system is evaluated, particularly for use as a barrier material to enable Al-contacting of GaN diodes. These Al-B diodes could provide an option for fabricating low-leakage diodes that are compatible with complementary metal-oxide-semiconductor (CMOS) processing at industrially attractive high throughput. The bulk B has high resistivity, which, combined with the fact that non-uniformities in the nm range, are typical due to gas depletion along the furnace tube and gives uncontrollable, often high diode series resistance. A simulation study shows that Al-B could, nevertheless, be used as a gate stack in HEMTs for low-frequency power applications.