Crack formation in GaAs heteroepitaxial films on Si and SiGe virtual substrates

Abstract

We have determined the critical cracking thickness, or the thickness beyond which crack formation is favored, in GaAs films grown on Si and SiGe virtual substrates analytically and experimentally. The analytical model predicts a critical cracking thickness proportional to the biaxial modulus and the crack resistance of the GaAs film, and inversely proportional to the square of the thermal stress and a nondimensional crack resistance number Z. This Z number is determined by the mechanical properties of the GaAs film for a system without substrate damage, and is also determined by the mechanical properties of the substrate for a system with substrate damage. The experimentally determined critical thicknesses were in general greater than the analytically derived values due to the kinetic barriers to crack nucleation, which were not taken into consideration in the models. In addition, we have observed an asymmetric crack array formation, where arrays running in the 〈110〉 substrate off-cut direction are favored. We have also performed finite element modeling of the crack systems to study the evolution of thermal stress around crack planes in the GaAs film.

Electron Microscopy of Cracks in InxGa1-xAs/GaAs(001) Multi-Quantum Wells

“…They demonstrated that the cracks, which have exhibited a dierent density along [110] and [110] depending on the residual strain, occurred after growth, and however, that the cracks did not have an important contribution to the strain relaxation inside the structures. Yang et al [17] observed an asymmetric crack array formation, caused by high thermal mismatches between in GaAs lms grown on Si and SiGe virtual substrates. Murray et al [18] reported a simple model describing the formation of cracks and their structural properties in tensile strained epilayers.…”

“…Thermal strain depends on the thermal expansion coecients of the lm and substrate [21]. Especially, crack arrays in the thin lms are the result of high thermal mismatch [17]. Consequently, the strain energy in the structure can be relaxed via crack initiation [20].…”

GaAsP/InGaP heterojunction bipolar transistors grown by MOCVD

“…Lastly, the coefficient of thermal expansion (CTE) of GaAsP is lower than that of GaAs and closer to that of Si, reducing the likelihood of the III-V epi-layers cracking due to CTE mismatch between the films and the substrate. 8 In this work, we demonstrate GaAsP/InGaP transistors at a range of compositions from = 0.825 to = 1 (GaAs). These devices are grown on GaAs substrates rather than Si substrates.…”

A Structural Characterization of GaAs MBE Grown on Si Pillars

“…Additional problems arise for device applications in which the epitaxial structures have to be thick, such as in multi--junction solar cells, high brightness light-emitting diodes (LEDs) and power transistors. Here, dierent thermal expansion coecients of layers and substrates often cause wafer bowing [6] and layer cracking [7,8]. These may prohibit further wafer processing and/or cause device failure.…”