David J. Larkin

Site‐competition epitaxy for superior silicon carbide electronics

We present and discuss a novel dopant control technique for compound semiconductors, called site‐competition epitaxy, which enables a much wider range of reproducible doping control and affords much higher and lower epilayer doping concentrations than was previously possible. Site‐competition epitaxy is presented for the chemical vapor deposition of 6H‐SiC epilayers on commercially available (0001)SiC silicon‐face substrates. Results from utilizing site‐competition epitaxy include the production of degenerately doped SiC epilayers for ohmic‐as‐deposited (i.e., unannealed) metal contacts as well as very low doped epilayers for electronic devices exhibiting SiC record‐breaking reverse voltages of 300 and 2000 V for 3C‐ and 6H‐SiC p‐n junction diodes, respectively.

2000 V 6H‐SiC p‐n junction diodes grown by chemical vapor deposition

In this letter we report on the fabrication and initial electrical characterization of the first silicon carbide diodes to demonstrate rectification to reverse voltages in excess of 2000 V at room temperature. The mesa structured 6H‐SiC p+n junction diodes were fabricated in 6H‐SiC epilayers grown by atmospheric pressure chemical vapor deposition on commercially available 6H‐SiC wafers. The devices were characterized while immersed in FluorinertTM to prevent arcing which occurs when air breaks down under high electric fields. The simple nonoptimized diodes, whose device areas ranged from 7×10−6 to 4×10−4 cm2, exhibited a 2000 V functional device yield in excess of 50%.

Surface morphology of silicon carbide epitaxial films

Silicon carbide (SiC) semiconductor technology has been advancing rapidly, but there are numerous crystal growth problems that need to be solved before SiC can reach its full potential. Among these problems is a need for an improvement in the surface morphology of epitaxial films that are grown to produce device structures. Because of advantageous electrical properties, SiC development is shifting from the 6H to the 4H polytype. In this study of both 6H and 4H-SiC epilayers, atomic force microscopy and other techniques were used to characterize SiC epilayer surface morphology. Observed features included isolated growth pits a few micrometers in size in both polytypes and triangles (in 4H only) approximately 50 um in size for epilayers 3 um in thickness. Also observed in some epilayers were large steps with heights greater than 20 nm. We found that there are significant differences between the morphology of 6H and 4H epilayers grown under identical conditions. We were able to improve surface morphology by avoiding conditions that lead to excess silicon during the initial startup of the growth process. However, the observed morphological defect density in both 6H and 4H epilayers was still the order of 104 cm-2 and varied widely from run to run. As expected, we found that morphological defects in the SiC substrates play a role in the formation of some epilayer surface features.

Hydrogen incorporation in boron-doped 6H-SiC CVD epilayers produced using site-competition epitaxy

We report on the initial investigations of using site-competition epitaxy to control boron incorporation in chemical vapor deposition (CVD) 6H-SiC epilayers. Also reported herein is the detection of hydrogen in boron-doped CVD SiC epilayers and hydrogen-passivation of the boron-acceptors. Results from low temperature photoluminescence (LTPL) spectroscopy indicate that the hydrogen content increased as the capacitance-voltage (C-V) measured net hole concentration increased. Secondary ion mass spectrometry (SIMS) analysis revealed that the boron and the hydrogen incorporation both increased as the Si/ C ratio was sequentially decreased within the CVD reactor during epilayer growth. Epilayers that were annealed at 1700°C in argon no longer exhibited hydrogen-related LTPL lines, and subsequent SIMS analysis confirmed the outdiffusion of hydrogen from the boron-doped SiC epilayers. The C-V measured net hole concentration increased more than threefold as a result of thel700°C anneal, which is consistent with hydrogen passivation of the boron-acceptors. However, boron related LTPL lines were not observed before or after the 1700°C anneal.

Aluminum acceptor four particle bound exciton complex in 4H, 6H, and 3C SiC

New lines in the low temperature luminescence spectra of lightly aluminum doped p‐type films of 3C, 6H, and 4H SiC are identified and associated with the recombination of a neutral aluminum acceptor four particle bound exciton complex.

Evidence for phosphorus on carbon and silicon sites in 6H and 4H SiC

New lines are observed in the photoluminescence of 6H and 4H SiC epitaxial layers grown in cold wall CVD reactors and doped with phosphorus. These lines are associated with neutral phosphorus donor four particle bound exciton complexes with the phosphorus substituting on both the carbon and silicon sublattices. Assignments are made for the (h) hexagonal and (k) cubic sites of the phosphorus donor substituting on the two SiC sublattices.