Disk configuration creates compact quantum cascade lasers operating at low currents

Researchers at Lucent Technologies (Murray Hill, NJ) have fabricated quantum cascade (QC) lasers in disk form, obtaining tiny mid-infrared-emitting devices that operate at low threshold currents. In quantum cascade lasers, electrons tumble between upper and lower energy levels in a quantum well, emitting photons; well thickness determines the emission wavelength. The QC disk lasers consist of 20 periods of gallium indium arsenide/aluminum indium arsenide (GaInAs/AlInAs) layers, each containing t

Disk configuration creates compact quantum cascade lasers operating at low currents

Researchers at Lucent Technologies (Murray Hill, NJ) have fabricated quantum cascade (QC) lasers in disk form, obtaining tiny mid-infrared-emitting devices that operate at low threshold currents. In quantum cascade lasers, electrons tumble between upper and lower energy levels in a quantum well, emitting photons; well thickness determines the emission wavelength. The QC disk lasers consist of 20 periods of gallium indium arsenide/aluminum indium arsenide (GaInAs/AlInAs) layers, each containing three quantum-well active regions alternating with superlattice injectors. This stack is sandwiched between GaInAs/AlInAs waveguide layers, and the whole structure is grown on an n+-doped indium phosphide (InP) substrate.

After lithographically producing the quantum cascade structure, the grou¥etched the wafer, undercutting the quantum cascade region to produce 1.69-µm-thick disks on In¥pedestals. Operational devices with disk diameters ranging from 17 to 80 µm were fabricated and tested, the 80-µm disk producing approximately 1 µW of output at 5 µm. Threshold current increases as a function of disk area; currents ranged from 2.85 mA for a 17-µm disk to 48.4 mA for a 75-µm disk. The devices operated u¥to a temperature of 150 K. Light output increased linearly as a function of current until applied current reached twice threshold; the reduced slope that appears in the plot at that point may be caused by spatial hole burning.

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