Leon Shterengas

Semiconductor photonic devices operating in the midwave infrared (mid-IR, which we roughly define here as wavelengths spanning 3 to 14 µm) uniquely address a wide range of current practical needs. These include chemical sensing, environmental monitoring, industrial process control, medical diagnostics, thermal imaging, LIDAR, free space optical communication, and security monitoring. However, mid-IR device technologies are currently still works in progress that are generally much less mature than their near infrared and visible counterparts. Not only are most of the relevant materials more difficult to grow and process, but attainment of the desired optical device performance is often fundamentally more challenging. This Roadmap will review the leading applications for mid-IR optoelectronics, summarize the status and deficiencies of current device technologies, and then suggest possible roadmaps for improving and maturing the performance, manufacturability, and cost of each device type so the critical needs that are uniquely addressed by mid-IR photonics can be satisfied.

Semiconductor photonic devices operating in the midwave infrared (mid-IR, which we roughly define here as wavelengths spanning 3 to 14 µm) uniquely address a wide range of current practical needs. These include chemical sensing, environmental monitoring, industrial process control, medical diagnostics, thermal imaging, LIDAR, free space optical communication, and security monitoring. However, mid-IR device technologies are currently still works in progress that are generally much less mature than their near infrared and visible counterparts. Not only are most of the relevant materials more difficult to grow and process, but attainment of the desired optical device performance is often fundamentally more challenging. This Roadmap will review the leading applications for mid-IR optoelectronics, summarize the status and deficiencies of current device technologies, and then suggest possible roadmaps for improving and maturing the performance, manufacturability, and cost of each device type so the critical needs that are uniquely addressed by mid-IR photonics can be satisfied.

Semiconductor photonic devices operating in the midwave infrared (mid-IR, which we roughly define here as wavelengths spanning 3 to 14 microns) uniquely address a wide range of current practical needs. These include chemical sensing, environmental monitoring, industrial process control, medical diagnostics, thermal imaging, LIDAR, free space optical communication, and security monitoring. However, mid-IR device technologies are currently still works in progress that are generally much less mature than their near infrared and visible counterparts. Not only are most of the relevant materials more difficult to grow and process, but attainment of the desired optical device performance is often fundamentally more challenging. This Roadmap will review the leading applications for mid-IR optoelectronics, summarize the status and deficiencies of current device technologies, and then suggest possible roadmaps for improving and maturing the performance, manufacturability, and cost of each device type so the critical needs that are uniquely addressed by mid-IR photonics can be satisfied.

The III–V-Sb separate absorption and multiplication (SAM) avalanche photodiode (APD) devices optimized for hole-initiated impact ionization have been developed. The hole-initiated process was selected to benefit from minimal valence band offset between InAsSb absorber and AlGaAsSb multiplier sections. The heterostructure design of the device facilitated shallow mesa fabrication, thereby minimizing etched sidewall leakage current. We tested devices with varying widths of the multiplier sections, with the most effective performance observed in SAM APDs featuring a 300 nm-thick multiplier section. The devices had cutoff wavelength of ∼3.9 μm at 80 K and operated in a background limited regime up to ∼200 K. The avalanche breakdown voltage was approximately −17.7 V at 80 K, increasing with temperature at a rate of 9.7 mV/K. An efficient hole-initiated impact ionization process resulted in multiplication gain values nearing one thousand, leading to peak values of current responsivity exceeding 50 A/W. It was observed that extensive tunneling occurs within the bias range between punch-through and avalanche breakdown, presumably due to the penetration of the electric field into the narrow bandgap absorber.

This study presents the molecular beam epitaxy growth of the indium-rich InGa0.2AsSb0.27 alloy with a 0.26 eV bandgap, lattice-matched (LM) to GaSb. A significant finding is the high material metrics, particularly the minority carrier lifetime (0.3 μs) and the background carrier concentration (8 × 1015 cm−3), in which the product reaches half the value of the reference InAsSb0.09 alloy. This indicates the suitability of indium-rich InGaxAsSby alloys LM to GaSb for low-dark-current, high-quantum-efficiency detectors for the entire mid-wave infrared wavelength range.

The GaSb-based epitaxially regrown monolithic diode PCSELs operating near 2 μm at room temperature in continuous wave regime and generating 30 mW of output power from 200 μm diameter aperture have been designed and fabricated. The devices demonstrated CW threshold current density of about 500 A/cm². The laser output power was enhanced thanks to increased buried void area fill-factor in the photonic crystal layer with multiple voids per unit cell. The PCSEL generated ultra-low divergence donut shape beams at the currents near threshold. At higher injection currents, the device brightness was limited by excitation of the higher order lateral modes. Generation of the vector-vortex beams of different types by different band edge states of the buried photonic crystal was observed.

Continuous wave room temperature operation of 2 μm GaSb-based photonic-crystal surface-emitting diode lasers has been realized. The deep etched square mesa devices showed threshold current densities of 500 A/cm2 at 20 °C. The epi-side down mounted lasers generated above 10 mW of output power in the continuous wave regime and tens of milliwatts in pulses from the 200 × 200 μm2 aperture. The breakthrough in the device performance parameters was achieved thanks to a highly homogeneous air-pocket retaining epitaxial regrowth process optimized for a specifically designed antimonide diode laser heterostructure. The nanofabrication method utilizing low temperature atomic hydrogen surface cleaning yielded low disorder square lattice of droplet-shaped voids covered by uniform p-cladding layer. The laser emission spectrum as well as near/far field patterns demonstrated peculiar features presumably linked to deformation of the void shape during regrowth and formation of the array of filaments.

Building upon recent advances in GaSb-based diode lasers and Er-doped fluoride fibre technologies, this article demonstrates for the first time the fibre-based amplification of mid-infrared diode lasers in the wavelength range around 2.78 $\mu \mathrm{m}$ . The laser setup consists of a GaSb-based diode laser and a single-stage Er-doped fibre amplifier. Amplification is investigated for continuous wave (CW) and ns-pulsed input signals, generated by gain-modulation of the GaSb-based seed lasers. The experimental results include the demonstration of output powers up to 0.9 W, pulse durations as short as 20 ns, and pulse repetition rates up to 1 MHz. Additionally, the amplification of commercial and custom-made GaSb-based seed lasers is compared and the impact of different fibre end-cap materials on laser performance is analysed.

Room temperature continuous wave operation of 2 µm photonic crystal surface emitting lasers (PCSELs) is reported. The GaSb-based PCSELs fabricated using highly uniform air-pocket retaining regrowth technology demonstrated threshold current densities of 500 A/cm² and generated tens of mW of output power at 20 °C.

Epitaxially regrown electrically pumped photonic crystal surface emitting lasers (PCSELs) operating near 2 µm were designed and fabricated within a III-V-Sb material system. A high-index-contrast photonic crystal layer was incorporated into the laser heterostructures by air-pocket-retaining epitaxial regrowth. Transmission electron microscopy studies confirmed uniform and continuous AlGaAsSb initial growth over the nano-patterned GaSb surface, followed by the development of the air-pockets. The PCSEL threshold current density had a minimal value of ~170 A/cm² in the 160–180 K temperature range when the QW gain spectrum aligned with the Γ₂ band edge of the photonic crystal. The devices operated in a continuous wave regime at 160 K. The divergence and polarization of the multimode laser beam emitted from the 200 µm × 200 µm PCSEL aperture were controlled by filamentation.