High-performance evanescently edge coupled photodiodes with partially p-doped photoabsorption layer at 1.55-μm wavelength

We demonstrate a high-performance evanescently coupled photodiode (ECPD) with the partially p-doped photoabsorption layer. As compared to the control ECPD with the traditional intrinsic photoabsorption layer, the demonstrated device can exhibit much higher output saturation current (power) and electrical bandwidth without sacrificing the quantum efficiency performance. By properly designing the geometry size and epilayer structures of the partially p-doped ECPD, very high responsivity (1.01 A/W), high electrical bandwidth (around 50 GHz), and high saturation current bandwidth product (920 mA/spl middot/GHz, at 40 GHz) have been achieved simultaneously at 1.55-μm wavelength.

There are two major trends to meet the challenge of photodetectors (PDs) with wide electrical bandwidth, high responsivity, and high output saturation power performance [1]. Fig. 1. (a) Cross-sectional view and (b) top view of demonstrated ECPDs. One is to distribute and uniform the photocurrents along the edge-coupled PDs, such as, velocity matched distributed photodetector [2] and evanescent coupled photodiode (ECPD) [3]–[5]; the other is to minimize the space-charge effect in the photoabsorption volume by changing the structure or material of epitaxial layers, such as unitraveling carrier PD [6], partially depleted absorber photodiode [7], and low-temperature-grown GaAs-based PDs [8]. However, the quantum efficiency performance of PDs with high saturation power are usually sacrificed due to its thin intrinsic layer or the recombination process of photogenerated carriers in the photoabsorption layer with p-type dopant or high density of defect [1], [8]. Recently, Muramoto and Ishibashi have demonstrated a new photodiode design that combines the depleted and neutral absorption layers (p-type doping) to maximize the bandwidth-efficiency product of photodiode [9]. In this work, we incorporated the partially p-doped photoabsorption layer and the evanescently edge-coupled waveguide structure of photodiode [10] to maximize its electrical bandwidth, quantum efficiency, and the capability of radio-frequency (RF) power generation. As compared to the control ECPD with the traditional intrinsic photoabsorption layer, the demonstrated ECPD with p-doped photoabsorption layer can achieve superior high-power performance without sacrificing the quantum efficiency. Very high responsivity (1.01 A/W), high electrical bandwidth (around 50 GHz), and high saturation current bandwidth product performances (more than 920 mA GHz at 40 GHz) have been achieved simultaneously at 1.55-m wavelength regime.