Relaxed GaP on Si with low threading dislocation density

We demonstrate a two-step procedure for the growth of relaxed GaP on pseudomorphic GaP/Si templates with a threading dislocation density (TDD) of 1.0-1.1 × 10⁶ cm^-2. In lattice-mismatched epitaxy, suppressed dislocation nucleation and unimpeded dislocation glide during relaxation are both critical to achieve a low TDD. Our two-step growth process realizes the former by initiating growth with a thin, low growth temperature (T_growth) layer and the latter with a subsequent high-T_growth layer. In optimizing the low-T_growth layer thickness, we find a trade-off where too little thickness does not suppress dislocation nucleation, while too much thickness takes away the advantage of higher dislocation velocity at high-T_growth. Dislocation pileups and trenches are identified as heterogeneous features with a very high local TDD that commonly arise during single-step growth of GaP on Si at high-T_growth, and two-step growth virtually eliminates their formation. Overall, this work shows that after initiation at low-T_growth, subsequent epitaxy can be performed at high-T_growth while avoiding rampant dislocation nucleation, as well as formation of trenches and dislocation pileups.