Introduce InGaAs photodetector

Introduce InGaAs photodetector

InGaAs is one of the ideal materials for achieving high-response and high-speed photodetector. Firstly, InGaAs is a direct bandgap semiconductor material, and its bandgap width can be regulated by the ratio between In and Ga, enabling the detection of optical signals of different wavelengths. Among them, In0.53Ga0.47As is perfectly matched with the InP substrate lattice and has a very high light absorption coefficient in the optical communication band. It is the most widely used in the preparation of photodetector and also has the most outstanding dark current and responsivity performance. Secondly, both InGaAs and InP materials have relatively high electron drift velocities, with their saturated electron drift velocities both approximately being 1×107cm/s. Meanwhile, under specific electric fields, InGaAs and InP materials exhibit electron velocity overshoot effects, with their overshoot velocities reaching 4×107cm/s and 6×107cm/s respectively. It is conducive to achieving a higher crossing bandwidth. At present, InGaAs photodetectors are the most mainstream photodetector for optical communication. In the market, the surface-incident coupling method is the most common. Surface-incident detector products with 25 Gaud/s and 56 Gaud/s can already be mass-produced. Smaller-sized, back-incident, and high-bandwidth surface-incident detectors have also been developed, mainly for applications such as high speed and high saturation. However, due to the limitations of their coupling methods, surface incident detectors are difficult to integrate with other optoelectronic devices. Therefore, with the increasing demand for optoelectronic integration, waveguide coupled InGaAs photodetectors with excellent performance and suitable for integration have gradually become the focus of research. Among them, commercial InGaAs photodetector modules of 70GHz and 110GHz almost all adopt waveguide coupling structures. According to the difference in substrate materials, waveguide coupled InGaAs photodetectors can mainly be classified into two types: INP-based and Si-based. The material epitaxial on InP substrates has high quality and is more suitable for the fabrication of high-performance devices. However, for III-V group materials grown or bonded on Si substrates, due to various mismatches between InGaAs materials and Si substrates, the material or interface quality is relatively poor, and there is still considerable room for improvement in the performance of the devices.

The stability of photodetector in various application environments, especially under extreme conditions, is also one of the key factors in practical applications. In recent years, new types of detectors such as perovskite, organic and two-dimensional materials, which have attracted much attention, still face many challenges in terms of long-term stability due to the fact that the materials themselves are easily affected by environmental factors. Meanwhile, the integration process of new materials is still not mature, and further exploration is still needed for large-scale production and performance consistency.

Although the introduction of inductors can effectively increase the bandwidth of devices at present, it is not popular in digital optical communication systems. Therefore, how to avoid negative impacts to further reduce the parasitic RC parameters of the device is one of the research directions of high-speed photodetector. Secondly, as the bandwidth of waveguide coupled photodetectors keeps increasing, the constraint between bandwidth and responsivity begins to emerge again. Although Ge/Si photodetectors and InGaAs photodetector with a 3dB bandwidth exceeding 200GHz have been reported, their responsivities are not satisfactory. How to increase bandwidth while maintaining good responsivity is an important research topic, which may require the introduction of new process-compatible materials (high mobility and high absorption coefficient) or novel high-speed device structures to solve. In addition, as the device bandwidth increases, the application scenarios of detectors in microwave photonic links will gradually increase. Unlike the small optical power incidence and high-sensitivity detection in optical communication, this scenario, on the basis of high bandwidth, has a high saturation power demand for high-power incidence. However, high-bandwidth devices usually adopt small-sized structures, so it is not easy to fabricate high-speed and high-saturation-power photodetectors, and further innovations may be needed in the carrier extraction and heat dissipation of the devices. Finally, reducing the dark current of high-speed detectors remains a problem that photodetectors with lattice mismatch need to solve. Dark current is mainly related to the crystal quality and surface state of the material. Therefore, key processes such as high-quality heteroepitaxy or bonding under lattice mismatch systems require more research and investment.