Size tunable Ge quantum dots for near-ultraviolet to near-infrared photosensing with high figures of merit

Abstract

We report a unique approach for the inclusion of size-tunable (7–50 nm), spherical Ge quantum dots (QDs) into gate stacks of metal-oxide-semiconductor (MOS) diodes, through selective oxidation of SiGe layers over the buffer layer of Si₃N₄ deposited over the Si substrate. In this complementary MOS (CMOS)-compatible approach, we successfully realized high performance nm scale Ge-QD MOS photodetectors with high figures of merit of low dark current density (1.5 × 10⁻³ mA cm⁻²), superior photo-current-to-dark current ratio (13 500), high photoresponsivity (2.2 A W⁻¹), and fast response time (5 ns), which are ready for direct integration with Si CMOS electronic circuits. Most importantly, the detection wavelength of the Ge QDs is tunable from near infrared to near ultraviolet by reducing the QD size from 50 to 7 nm as well as the optimal photoresponsivity is tailored by the Ge QD size and the effective thickness of gate dielectrics.