Resonant-cavity-enhanced responsivity in germanium-on-insulator photodetectors

Abstract

The germanium-on-insulator (GOI) has recently emerged as a new platform for complementary metal-oxide-semiconductor (CMOS)-compatible photonic integrated circuits. Here we report on resonant-cavity-enhanced optical responses in Ge photodetectors on a GOI platform where conventional photodetection is difficult. A 0.16% tensile strain is introduced to the high-quality Ge active layer to extend the photodetection range to cover the entire range of telecommunication C- and L-bands (1530–1620 nm). A carefully designed vertical cavity is created utilizing the insulator layer and the deposited SiO2 layer to enhance the optical confinement and thus optical response near the direct-gap absorption edge. Experimental results show a responsivity peak at 1590 nm, confirming the resonant cavity effect. Theoretical analysis shows that the optical responsivity in the C- and L-bands is significantly enhanced. Thus, we have demonstrated a new type of Ge photodetector on a GOI platform for CMOS-compatible photonic integrated circuits for telecommunication applications.

High Performance p-i-n Photodetectors on Ge-on-Insulator Platform

“…A/W at −1 V obtained by laser under 1310 nm, 1550 and 1630 nm are also shown comparison. The trend of spectral response is consistent with that measured by la Compared to the other Ge PDs reported previously [18,26,36], this GOI detector achie high responsivity in a wide spectral range of 1200~1650 nm. The responsivity spectrum GOI PD showed strong oscillation structures, indicating the effectiveness of the reson cavity structure to enhance the responsivity.…”

“…Due to the high refractive contrast between Ge(n~4.2), SiO 2 (n~1.45), and Si(n~3.42), the light propagating in the Ge active layer can experience strong reflection at the Ge/insulator/Si interfaces, achieving better optical confinement in the GOI structure [ 18 ]. Due to the resonant cavity effect, the light intensity in the GOI active layer is higher than that of Ge on Si under the same light power irradiation, so the photocurrent of GOI PD is higher than that of Ge-on-Si PD.…”

“…The black, red, and blue lines represent the saturated photocurrents curves of the Ge-on-Si PD, GOI PD without TEOS, and GOI PD with TEOS with the same diameter of 80 μm, respectively. Compared to the Ge-on-Si PD, the saturated photocurrent of the GOI PD without TEOS was improved from 17 to 19 mA at −1 V. The saturated photocurrent of the GOI PD with TEOS seemed to be higher than 40 mA when the incident light power exceeded 100 mW, which is twice that of the GOI PD without TEOS at −1 V. Due to the high refractive contrast between Ge(n~4.2), SiO2(n~1.45), and Si(n~3.42), the light propagating in the Ge active layer can experience strong reflection at the Ge/insulator/Si interfaces, achieving better optical confinement in the GOI structure [18]. Due to the resonant cavity effect, the light intensity in the GOI active layer is higher than that of Ge on Si under the same light power irradiation, so the photocurrent of GOI PD is higher than that of Ge-on-Si PD.…”

“…In ref [ 17 ], the leakage current of Ge p-i-n photodiodes on a GOI substrate with threading dislocation density (TDD) of ~3.2 × 10 6 cm −2 was reduced by 53-fold from one with a TDD of ~5.2 × 10 8 cm −2 . In addition, the introduction of an insulator layer between the Si and Ge can provide better optical confinement for the Ge active layer, enhancing the optical responses of the devices [ 18 ]. The direct absorption edge of Ge at 1550 nm limits the application of Ge PD in the C-band (1530–1560 nm) and L-band (1560–1625 nm).…”

Metal-Semiconductor-Metal GeSn Photodetectors on Silicon for Short-Wave Infrared Applications

“…To obtain a clear visualization of the effect of Sn concentration on the absorption coefficient, we theoretically calculated the strained electronic band structures using the deformation potential theory [ 42 , 48 ]. Then, the direct band absorption coefficient was calculated by using the Fermi’s golden rule with consideration of a Lorentzian lineshape function [ 25 , 49 ], where n r is the refractive index; c is the velocity of light in free space; e is the electronic charge; ħ is the reduced Planck’s constant; m 0 is the rest mass of an electron; ɛ 0 is the free space permittivity; ω is the angular frequency of incident light; is the momentum matrix; γ is the full-width-at-half-maximum (FWHM) of the Lorentzian lineshape, whose value 15 meV was used in this study; E CΓ ( k ) and E m ( k ) are the electron and hole energy in the Γ-valley conduction band (CB) and valance band (VB), respectively, which were calculated using a multi-band k·p method by considering the strain effect [ 33 , 42 ]. The summation over m represents all interband transitions from the VB (HH and LH bands) to the direct CB.…”