Uni-traveling-carrier photodetector with high-contrast grating focusing-reflection mirrors

Abstract

A novel uni-traveling-carrier photodetector (UTC-PD) structure with an integrated focusingreflection (FR) mirror realized by a non-periodic concentric circular high-contrast grating (NP-CC-HCG), referred to as FR-UTC-PD, is proposed to enhance responsivity in conventional UTC-PDs. The FR-UTC-PD allows improving the responsivity by 36.5% at a 1.55-μm wavelength as compared to a UTC-PD without integrated an FR mirror with 84.59% reflectivity. For 40-μm-diameter PDs, the obtained 3-dB bandwidths are unaltered with values of 18 GHz at -3.0 V bias voltage. The radio-frequency (RF) output power and photocurrent are -1.77 dBm and 17.56 mA, respectively, at 10 GHz and the -6.0 V bias voltage. Submitted To APEX 2The high-speed and high-responsivity photodetectors operating at long wavelength regimes have been widely used in wireless communication system, broadband optical communication system, and high-frequency measurement systems. 1-2) The uni-travelingcarrier photodetector (UTC-PD) [3][4] only utilizes electrons as active carriers and thus easily exhibits high-speed and high-output characteristics simultaneously, which has been of great interest both for research [5][6][7][8] and broad ranges of applications. 9-14) Moreover, high-speed UTC-PDs also need high-responsivity to prevent the waveform distortion of the high-speed signals and thus degrade the total power consumption of the system. Therefore, it is very important to adopt methods to further improve the bandwidth and responsivity performance for UTC-PDs. For instance, a UTC-PD with the downscaling absorber thickness and absorption area starting with 86 nm, 13μm 2 scaled down to 30 nm, 5 μm 2 , achieves 3-dB bandwidths from 235 GHz to 310 GHz while having the responsivities from 0.126 A/W to 0.07 A/W, respectively, at a 1.55-μm wavelength. [5][6] In order to achieve higher responsivity, a UTC-PD with a 1.2-μm-thick InGaAs absorber exhibits the responsivity up to 1.0 A/W, with a 3-dB bandwidth of only 9 GHz under low photocurrent. 15) Hence, balancing the tradeoff between the bandwidth and responsivity in UTC-PDs has become an active research area.Recently, various structures have been explored to address the bandwidth-responsivity

Advances in High–Speed, High–Power Photodiodes: From Fundamentals to Applications

“…Furthermore, the optical-to-electrical (O/E) conversion efficiency and heat dissipation at a high bias voltage also needs to be considered. We could use resonant cavity enhanced (RCE) structure [33] employing distributed Bragg reflector (DBR) [34], subwavelength grating (SWG) mirrors [35] as bottom reflectors and dielectric layers as top reflectors to increase O/E conversion efficiency, while using high conductivity AlN [36,37], diamond [38] or SiC [39] substrates to reduce heat dissipation. Moreover, the slow light effect resulting from Bragg grating structures [40,41] with a remarkably low group velocity might offer a possible and promising solution to successfully compress optical signals and enhance light-matter interactions, and the enhanced O/E conversion efficiency in PDs could be possible while the joule heat problem at a higher bias voltage, device footprint reduction, and low power consumption could also be solved in the future.…”

Experimental Demonstration of Light Focusing Enabled by Monolithic High-Contrast Grating Mirrors

“…In all four of these constructions, the incident and reflected light propagated in air. In another mirror, reported by Chen et al, 17 the incident and reflected light propagated in InP and the grating was made of Si. However, as in the previous cases, InP has a lower refractive index than the grating.…”

“…However, as in the previous cases, InP has a lower refractive index than the grating. In ref ( 17 ), the focal length was around 400 μm. No information was given on the light intensity at the focal point relative to the incident light intensity.…”

“…Nonetheless, the light intensity at the focal point shown in this article is over an order of magnitude higher than any reported for a focusing mirror previously in the literature. 15 , 16 Out of five reports on focusing grating mirrors, 13 − 17 only two 15 , 16 provide information on the light intensity relative to the incident light intensity at the focal point, which is 1.2 at best.…”

High speed evanescent waveguide photodetector with a 100 GHz bandwidth

“…[14][15][16] They utilize the electron overshoot velocity and hole relaxation to reduce the total carrier transit time, meanwhile featuring high response linearity. A drawback of this structure is relatively low responsivity to the conventional P-I-N doping type structure due to the compressed absorption layer, 17,18) and thus the appearance of a modified UTC structure with a cliff layer to balance carrier transit-times and quantum efficiency. [19][20][21] In this work, a waveguide PD with a 100 GHz bandwidth is reported.…”