In the Nov. 1 issue of Applied Physics Letters, engineers at Stanford University in California report the development of a two-color InGaAs quantum-dot infrared photodetector that operates at 5.5 and 9.2 µm at 77 K. Potential applications of the device include temperature sensing, chemical analysis and target discrimination.

The detector comprises 10 layers of N-doped InGaAs quantum dots in an InGaP matrix, sandwiched between GaInP barrier layers and GaAs. The quantum dots display an average radius of 20 nm and an areal density of 3 × 10¹⁰/cm². The researchers fabricated the device by low-pressure metallorganic chemical vapor deposition.

Fourier transform IR spectroscopy revealed that the spectral response of the detector depends on the bias voltage, with its 9.2-µm response peaking at 20.8 V and disappearing beyond 21.2 V. Measured dark currents at various bias voltages were as low as 0.03 pA for 20.1 V. Calculated peak detectivities were 4.7 × 10⁹ cm Hz^1/2/W at 5.5 µm and 7.2 × 10⁸ cm Hz^1/2/W at 9.2 µm.