Inter-subband detectors such as quantum well infrared photodetectors (QWIP) have been widely used in infrared remote sensing. Quantum dot infrared photodetectors (QDIPS) have been predicted to have better performanc than QWIPs due to the novel properties of quantum dots caused by the extra confinement. Here we report our recent results of InAs QDIP grown on InP substrate by low-pressure metalorganic chemical vapor deposition. The device structure consists of multiple stacks of InAs quantum dots with GaAs/AlInAs/InP barrier. 400μx400μm test mesas were fabricated for device characterizations. Photoresponse was observed with a peak wavelength of 6.4 μm and a cutoff wavelength of 6.6 μm at both 77K and 100K. A detectivity of 1.0x10<sup>10</sup> cmHz<sup>1/2</sup>/W was obtained at 77K at a bias of -1.1. V. To the best of our knowledge, this is the highest detectivity reported for InAs QDIP grown on InP substrate. At 100K, the detectivity only drops to 2.3x10<sup>9</sup>cmHz<sup>1/2</sup>/W.
InGaAs/InGaP quantum-dots have been grown by low-pressure metalorganic chemical vapor deposition technique on GaAs substrate. The important growth parameters, such as growth temperature, V/III ratio, etc, have been optimized. A 10-stack quantum-dot infrared photodetector based on these InGaAs dots showed a detectivity of 3.6x10<sup>10</sup> cmHz<sup>1/2</sup>/W at 95K. The peak photoresponse was 4.7 μm with a cutoff at 5.2μm. A 256x256 middle-wavelength infrared focal plane array based on our quantum-dot detectors was fabricated via dry etching technique. The detector array was bonded to a silicon readout integrated circuit via flip chip bonding with indium bumps. A noise equivalent temperature difference of 509 mK was achieved for this array at 120K. With the goal of improving array uniformity, exploratory work into nanopillar structure IR detectors was also performed. Experimental methods and characterization results are presented here.
The authors report the most recent progress in Type II InAs/GaSb superlattice materials and photovoltaic detectors developed for focal plane array applications with a cutoff wavelength of ~8 μm. No turn-on of tunneling current was observed even at a reverse bias of -3 V for a 3 μm thick p-i-n photodiodes. The thermally-limited zero bias detectivity under 300 K 2 π FOV was 2~3×10<sup>11</sup> cm•Hz<sup>1/2</sup>/W at liquid nitrogen temperature, with a current responsivity of 2~3 A/W and a mean quantum efficiency of ~50%. Initial passivation using SiO<sub>2</sub> has shown to decrease the dark current by ~30% at a reverse bias of -1 V. The same detector structure was used for focal plane arrays with silicon readout integrated circuit. Concept proof of imaging was demonstrated with a format of 256×256 at liquid nitrogen temperature.