Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Abstract

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain-relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN-on-Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack-free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 cm achieved to date in GaN-on-Si is demonstrated. With these advances, the first vertical GaN metal-insulator-semiconductor field-effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost-effective high power device paradigm on an Si CMOS platform are demonstrated.

MOVPE growth of GaN on patterned 6-inch Si wafer

“…The obtained biaxial stresses are not high and are comparable to the previous research [12]. The small stress difference could be explained by the different temperature in the center and edge of the substrate during GaN growth.…”

“…This allows us to see in figure 9 that GaN in the round corner mesa (b) is slightly more tensile stressed than in the sharp corner mesa (a). The cross-sections In contrast to previous reports on the circle shaped mesas, where compressive strain is maximum at the center and relaxes towards all the edges [12,16], here stresses distribute uniformly for the whole square mesa surface. However, the slight asymmetry in figure 9(e) could be caused by an unintentional artifact of accumulated instrumental errors [17], since biaxial stress distributions in figures 9(a) and (b) tend their highest values towards the bottom-right corners.…”

“…Confocal Raman spectroscopy is a nondestructive and sensitive optical method for quantitative characterization of stress distribution in GaN layers via observing Raman peak shifts [12,[15][16][17]. Modern Raman tools operate close to the optical diffraction limit and are capable of detecting the local stresses with lateral spatial resolution of only 0.5 μm [18].…”

“…, where, in case of the Raman peak w » E , H 2 0 568 rel. cm −1 is a still-debated stress-free value [12,15] and K=4.2 cm −1 GPa −1 is an experimentally measured phonon deformation potential [12,23]. The Raman scattering was excited by a 488nm wavelength laser with 10 mW power, focused through an intermediate magnification/numerical aperture×20/0.4 dry objective lens.…”

“…So far, SAGs have extensively used rectangular growth patterns where the stresses peak at the pattern corners and it is at these corners where the crack in the GaN layers nucleates [9][10][11]. In a recent work, 19μm thick crack-free GaN layers on Si has been reported [12], where SAG was performed for circular patterns with 350μm diameter. As their thermal stress simulations showed, the corner stress is significantly reduced when more corners were added to the pattern and is lowest for a circular interface.…”