Resonant cavity-enhanced photodiode array for miniaturised spectroscopic sensing.

Optical spectroscopic sensing is a technique that is commonly employed for the identification and compositional analysis of a wide variety of substances, from biological samples to greenhouse gases. High-resolution spectrometers are well established, however, attempts to miniaturise the designs can suffer from adverse effects due to the miniaturisation, for both Fourier transform based interferometric designs, as well as dispersive designs. In this work, a linear array of resonant cavity-enhanced photodiodes is realised with spatially chirped resonance wavelength, offering chip-scale free-space hyperspectral sensing. Resonant cavity-enhanced photodiodes sense over a narrow spectral band, which can be tuned by the thicknesses of the heterostructure. Through this work, multiple narrow spectral bands can be sensed by resonant cavity-enhanced photodiodes on a single chip by grading the thicknesses across the wafer. Photocurrent measurements from a fabricated array determine the wavelength of incident light with an accuracy of ± 2 nm.

Mid-infrared resonant cavity light emitting diodes operating at 4.5†µm.

We report on a mid-infrared resonant cavity light emitting diode (RCLED) operating at the wavelength of 4.5 µm with a narrow spectral linewidth at room temperature. Compared to a reference LED without a resonant cavity, our RCLED exhibits (85x) higher peak intensity, (13x) higher integrated output power, (16x) narrower spectral linewidth and (7x) superior temperature stability. The device consists of a one-wavelength thick micro-cavity containing an Al0.12In0.88As/InAs0.85Sb0.15 quantum well active region sandwiched between two high contrast AlAs0.08Sb0.92/GaSb distributed Bragg reflector mirrors, grown lattice-matched on GaSb by molecular beam epitaxy. The high spectral brightness, narrow linewidth and superior temperature stability are attractive features, enabling these devices to be used for detection of N2O at 4.5 µm. We show that with only minor adjustments the gases CO2 (4.2 µm) and CO (4.6 µm) are also readily accessible.

Resonant cavity-enhanced photodetector incorporating a type-II superlattice to extend MWIR sensitivity.

Mid-infrared resonant cavity-enhanced photodetectors (RCE PD) present a promising technology for targeted gas detection. We demonstrate an RCE PD incorporating an InAs/InAsSb superlattice as the detecting element, extending the resonant wavelength beyond 4 µm. AlAsSb/GaSb mirrors and a unipolar barrier active region paralleling an nBn structure are also used, and performance is compared to a conventional broadband nBn detector incorporating the same superlattice. The RCE PD exhibited a Q-factor of ∼90 and an extremely stable resonance wavelength. Peak responsivity was 3.0 A W-1 at 240 K, equalling 84% quantum efficiency, a 5.5 times increase over the reference nBn at the same wavelength. Dark current density was 3.3×10-2 A cm-2 at 240 K, falling to 2.7×10-4 A cm-2 at 180 K. The broadband BLIP limit is approached at 180 K with specific detectivity of 2.1×1011 cm Hz1/2 W-1, which presents the potential of achieving BLIP-limited operation in the thermoelectric cooling regime.

Low Leakage-Current InAsSb Nanowire Photodetectors on Silicon.

Axially doped p-i-n InAs0.93Sb0.07 nanowire arrays have been grown on Si substrates and fabricated into photodetectors for shortwave infrared detection. The devices exhibit a leakage current density around 2 mA/cm(2) and a 20% cutoff of 2.3 µm at 300 K. This record low leakage current density for InAsSb based devices demonstrates the suitability of nanowires for the integration of III-V semiconductors with silicon technology.