Selective Area Growth of InGaAs/InP Quantum Well Nanowires on SOI Substrate
Authors: Li Yajie , Wang Mengqi , Fang Xin , Wang Pengfei , Wang Huolei , Li Zhaosong , Zhou Xuliang , Yu Hongyan , Chen Weixi , Pan Jiaoqing 
Published: February 2020

In recent years, silicon photonic integrated circuits have been extensively studied, which is becoming a promising platform for higher speed interconnect and complex higher functionality with low cost. However, silicon is of indirect bandgap, and thus extremely hard for light emitting, especially at room temperature. By using aspect-ratio trapping (ART) technique, selective area epitaxy of III–V materials on Si shows advantages for monolithic integration of III-Vs on silicon, with defects trapped at the bottom of epitaxial materials.

We have directly grown III-V nanowires with an InGaAs/InP quantum well (QW) in the V-grooves on SOI substrates by a MOCVD system. SOI substrates with an oxide layer buried are good at preventing a majority of light leak into the silicon underneath.Therefore a stable optical mode is supposed to be in the III-V nanowires when the scale of cross section down to subwavelength. A low temperature (LT) GaAs was initially deposited at 400 °C as a seeding layer. Then a high temperature (HT) GaAs at 630 °C was performed to fill V-grooves, and used as an intermediary layer for following InP growth, owing to the lattice mismatch of of GaAs to Si (4%) lower than that of InP to Si (8%). So the next performance was 400 °C LT-InP and 650 °C HT-InP growths on the bottom GaAs in trenches, leading to high quality of top InP. The following was the growth of a InGaAs quantum well layer and a InP capping layer. The In/Ga molar ratio of precursors in quantum-well growth was 1.1.

We measured the micro photoluminescence (μPL) spectra of the III-V nanowires with the InGaAs/InP quantum well at room temperature. Two large peaks were observed at around 1310 nm and 1550 nm. When the pump power is one tenth of the original, the peak around 1310 nm is greatly reduced, mainly leaving the peak near 1550 nm. The observed μPL spectra are mainly influenced by three factors——the thickness uniformity of the QW, the composition uniformity of the In atoms, and the energy of the pumping source. The InGaAs/InP QW grown by this method is of the "∧" shape, and the thickness of the QW is gradually thickened from the bottom to the top, causing the spectrum to broaden toward long wavelengths, If the InGaAs QW has the same elemental composition everywhere. However, when the InGaAs material is epitaxially grown on a non-planar structure, the In atoms move faster at the high-curvature surface. Therefore, the In composition of the InGaAs material in the top QW is relatively low, and the corresponding bandgap energy is larger. Since the composition of In atoms in the ∧-shaped QW is not a constant, resulting in the bandgap width of the QW is not a constant. When a laser beam penetrates into the QW, the hole electron pairs in the narrow bandgap recombines firstly to emit light of long wavelength. If the number of pump photons is sufficient, it will continue to excite the hole electron pairs in the wide bandgap to recombine, and emit light of short wavelength.

Figure 1