Silicon photonics (SiPh) enables compact photonic integrated circuits (PICs), showing superior performance for a wide variety of applications. Various optical functions have been demonstrated on this platform that allows for complex and powerful PICs. Nevertheless, laser source integration technologies are not yet as mature, hampering the further cost reduction of the eventual Si photonic systems-on-chip and impeding the expansion of this platform to a broader range of applications. Here, we discuss a promising technology, micro-transfer-printing (μTP), for the realization of III-V-on-Si PICs. By employing a polydimethylsiloxane elastomeric stamp, the integration of III-V devices can be realized in a massively parallel manner on a wafer without substantial modifications to the SiPh process flow, leading to a significant cost reduction of the resulting III-V-on-Si PICs. This paper summarizes some of the recent developments in the use of μTP technology for realizing the integration of III-V photodiodes and lasers on Si PICs.

We have optimized the molecular-beam epitaxy growth conditions of self-organized $\mathrm{InAs}∕\mathrm{GaAs}$ quantum dots (QDs) to achieve a low density of dots emitting at 1300 nm at low temperature. We used an ultralow InAs growth rate, lower than $0.002\mathrm{ML}∕\mathrm{s}$ , to reduce the density to $2\text{dots}∕\mu {\mathrm{m}}^2$ and an InGaAs capping layer to achieve longer emission wavelength. Microphotoluminescence spectroscopy at low-temperature reveals emission lines characteristic of exciton-biexciton behavior. We also study the temperature dependence of the photoluminescence, showing clear single QD emission up to 90 K. With these results, $\mathrm{InAs}∕\mathrm{GaAs}$ QDs appear as a very promising system for future applications of single photon sources in fiber-based quantum cryptography.

The development of ultralow-loss silicon-nitride-based waveguide platforms has enabled the realization of integrated optical filters with unprecedented performance. Such passive circuits, when combined with phase modulators and low-noise lasers, have the potential to improve the current state of the art of the most critical components in coherent communications, beam steering, and microwave photonics applications. However, the large refractive index difference between silicon nitride and common III-V gain materials in the telecom wavelength range hampers the integration of electrically pumped III-V semiconductor lasers on a silicon nitride waveguide chip. Here, we present an approach to overcome this refractive index mismatch by using an intermediate layer of hydrogenated amorphous silicon, followed by the microtransfer printing of a prefabricated III-V semiconductor optical amplifier. Following this approach, we demonstrate a heterogeneously integrated semiconductor optical amplifier on a silicon nitride waveguide circuit with up to 14 dB gain and a saturation power of 8 mW. We further demonstrate a heterogeneously integrated ring laser on a silicon nitride circuit operating around 1550 nm. This heterogeneous integration approach would not be limited to silicon-nitride-based platforms: it can be used advantageously for any waveguide platform with low-refractive-index waveguide materials such as lithium niobate.