offers a low-cost solution for high-speed interconnects for data transmission. The integration of high-quality direct-bandgap III-V lasers on Si platform is a core technology for achieving high-performance Si-based III-V optoelectronic devices, [1-3] due to the inefficient light-emitting properties of Group-IV materials. [4,5] Currently, the realization of III-V lasers on Si mainly relies on either wafer bonding or monolithic growth techniques, with the latter method being more favorable for low cost, high yield and large-scale production. [6,7] Nevertheless, the large lattice mismatch, different polarities and incompatible thermal expansion coefficients between III-V materials and Si induce various crystal defects during the epitaxial growth such as threading dislocations (TDs), inversion boundaries (IBs, often called anti-phase boundaries, APBs), and microcracks. [8-13] These defects act as non-radiative recombination centers and significantly hinder the performance of optoelectronic devices in terms of lifetime, threshold operating power and temperature performance. [2,7,14] Approaches including strained-layer superlattice (SLS) acting as a defect filter layer (DFL) and a longer cool-down period after growth were implemented to sufficiently suppress TDs and micro-cracks, respectively. [12,13,15] By contrast, IBs are electrically charged planar Monolithic integration of III-V materials and devices on CMOS compatible on-axis Si (001) substrates enables a route of low-cost and high-density Si-based photonic integrated circuits. Inversion boundaries (IBs) are defects that arise from the interface between III-V materials and Si, which makes it almost impossible to produce high-quality III-V devices on Si. In this paper, a novel technique to achieve IB-free GaAs monolithically grown on on-axis Si (001) substrates by realizing the alternating straight and meandering single atomic steps on Si surface has been demonstrated without the use of double Si atomic steps, which was previously believed to be the key for IB-free III-V growth on Si. The periodic straight and meandering single atomic steps on Si surface are results of high-temperature annealing of Si buffer layer. Furthermore, an electronically pumped quantum-dot laser has been demonstrated on this IB-free GaAs/Si platform with a maximum operating temperature of 120 °C. These results can be a major step towards monolithic integration of III-V materials and devices with the mature CMOS technology.
Semiconductor broadband light emitters have emerged as ideal and vital light sources for a range of biomedical sensing/imaging applications, especially for optical coherence tomography systems. Although near-infrared broadband light emitters have found increasingly wide utilization in these imaging applications, the requirement to simultaneously achieve both a high spectral bandwidth and output power is still challenging for such devices. Owing to the relatively weak amplified spontaneous emission, as a consequence of the very short non-radiative carrier lifetime of the inter-subband transitions in quantum cascade structures, it is even more challenging to obtain desirable mid-infrared broadband light emitters. There have been great efforts in the past 20 years to pursue high-efficiency broadband optical gain and very low reflectivity in waveguide structures, which are two key factors determining the performance of broadband light emitters. Here we describe the realization of a high continuous wave light power of >20 mW and broadband width of >130 nm with near-infrared broadband light emitters and the first mid-infrared broadband light emitters operating under continuous wave mode at room temperature by employing a modulation p-doped InGaAs/GaAs quantum dot active region with a ‘J’-shape ridge waveguide structure and a quantum cascade active region with a dual-end analogous monolithic integrated tapered waveguide structure, respectively. This work is of great importance to improve the performance of existing near-infrared optical coherence tomography systems and describes a major advance toward reliable and cost-effective mid-infrared imaging and sensing systems, which do not presently exist due to the lack of appropriate low-coherence mid-infrared semiconductor broadband light sources.
A high-performance III-V quantum-dot (QD) laser monolithically grown on Si is one of the most promising candidates for commercially viable Si-based lasers. Great efforts have been made to overcome the challenges due to the heteroepitaxial growth, including threading dislocations (TDs) and anti-phase boundaries (APBs), by growing a more than 2 µm thick III-V buffer layer. However, this relatively thick III-V buffer layer causes the formation of thermal cracks in III-V epi-layers, and hence a low yield of Si-based optoelectronic devices. In this paper, we demonstrate a usage of thin Ge buffer layer to replace the initial part of GaAs buffer layer on Si to reduce the overall thickness of the structure, while maintaining a low density of defects in III-V layers and hence the performance of the InAs/GaAs QD laser. A very high operating temperature of 130 °C has been demonstrated for an InAs/GaAs QD laser by this approach.
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