S. R. Darvish

Room temperature continuous wave operation of quantum cascade lasers with 12.5% wall plug efficiency

An InP based quantum cascade laser heterostructure emitting at 4.6μm was grown with gas-source molecular beam epitaxy. The wafer was processed into a conventional double-channel ridge waveguide geometry with ridge widths of 19.7 and 10.6μm without semi-insulating InP regrowth. An uncoated, narrow ridge device with a 4.8mm cavity length was epilayer down bonded to a diamond submount and exhibits 2.5W maximum output power with a wall plug efficiency of 12.5% at room temperature in continuous wave operation.

High-power 280 nm AlGaN light-emitting diodes based on an asymmetric single-quantum well

We demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric single-quantum-well active layer configuration on top of a high-quality AlGaN/AlN template layer. An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 μm×300 μm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current.

Room temperature continuous wave operation of quantum cascade lasers with watt-level optical power

We demonstrate quantum cascade lasers at an emitting wavelength of 4.6μm, which are capable of room temperature, high power continuous wave (cw) operation. Buried ridge geometry with a width of 9.8μm was utilized. A device with a 3mm cavity length that was epilayer-down bonded on a diamond submount exhibited a maximum output power of 1.3W at room temperature in cw operation. The maximum output power at 80K was measured to be 4W, with a wall plug efficiency of 27%.

4.5 mW operation of AlGaN-based 267 nm deep-ultraviolet light-emitting diodes

We demonstrate 4.5 mW output power from AlGaN-based single quantum well ultraviolet light-emitting diodes at a very short wavelength of 267 nm in pulsed operation mode. The output power in continuous-wave mode reaches a value of 165 μW at an injected current of 435 mA. The measurements were done on arrays of four devices flip chip bonded to AlN submounts for thermal management.

Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency

The authors report on the development of λ∼4.7μm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150K, with continuous-wave output powers of more than 1W.

Temperature dependent characteristics of λ∼3.8μm room-temperature continuous-wave quantum-cascade lasers

Temperature dependent characteristics of λ∼3.8μm quantum-cascade lasers (QCLs) operating up to 318K in continuous-wave (cw) mode are reported. A high-reflectivity coated 11.5-μm-wide and 4-mm-long epilayer-down bonded QCL using a diamond submount shows a considerable improved cw operation with an output power of 143mW and a threshold current density of 1.51kA∕cm2 at 298K. The temperature dependence on optical and electrical performances of the QCLs with respect to the output power, slope efficiency, threshold current/voltage, turn-on voltage, differential series resistance, and emission wavelength are investigated systematically above liquid nitrogen temperature.

High-power, room-temperature, and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ∼4.8μm

A high-power continuous-wave (CW) operation of distributed-feedback quantum-cascade lasers using a buried grating with epitaxial regrowth up to temperatures of above 60°C is demonstrated. For a high-reflectivity-coated 13μm-wide and 3mm-long cavity, CW output powers of 135mW at 25°C and still 37mW at 60°C are obtained. The device exhibits a CW threshold current density of 1.1kA∕cm2, a maximum CW wall-plug efficiency of 1.48% at 25°C, and a characteristic temperature of 177K in pulsed mode. Single-mode emission near 4.8μm with a side-mode suppression ratio of >30dB and a tuning range of ∼8.1cm−1 (i.e., tunability of 0.18cm−1∕K) in the temperature range from 15to60°C is observed.

Top-emission ultraviolet light-emitting diodes with peak emission at 280 nm

We demonstrate light emission at 280 nm from UV light-emitting diodes consisting of AlInGaN/AlInGaN multiple quantum wells. Turn-on voltage of the devices is ∼5 V with a differential resistance of ∼40 Ω. The peak emission wavelength redshifts ∼1 nm at high injection currents.

Room-temperature continuous-wave operation of quantum-cascade lasers at λ∼4μm

High-power cw λ∼4μm quantum-cascade lasers (QCLs) are demonstrated. The effect of different cavity length and laser die bonding is also investigated. For a high-reflectivity-coated 11-μm-wide and 4-mm-long epilayer-down bonded QCL, cw output powers as high as 1.6W at 80K and 160mW at 298K are obtained, and the cw operation is achieved up to 313K with 12mW. The laser exhibits a threshold current density of 1.96kA∕cm2, a slope efficiency of 737mW∕A, and a maximum wall-plug efficiency of 0.9% under cw mode at 298K. In pulsed mode, a maximum average power of 552mW at 298K is achieved at 45% duty cycle and a characteristic temperature is 176K from 80to393K.

High quantum efficiency AlGaN solar-blind p-i-n photodiodes

We report AlGaN-based back-illuminated solar-blind ultraviolet p-i-n photodetectors with a peak responsivity of 136 mA/W at 282 nm without bias. This corresponds to a high external quantum efficiency of 60%, which improves to a value as high as 72% under 5 V reverse bias. We attribute the high performance of these devices to the use of a very-high quality AlN and Al0.87Ga0.13N/AlN superlattice material and a highly conductive Si–In co-doped Al0.5Ga0.5N layer.