Terahertz absorption in AlGaAs films and detection using heterojunctions

HEterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors using AlGaAs as both the emitter and the barrier material with different Al fractions for the two layers are demonstrated. The extension of the HEIWIP concept to wavelengths longer than 110 lm in the GaAs/AlGaAs system requires the use of AlGaAs as the emitter material to reduce the barrier height. The p-type doping produces an offset in the valance band between doped and undoped material. The Al fraction difference then gives a valance band offset in the opposite direction, which reduces the total offset. The FIR absorption up to 400 lm for AlGaAs films with different Al fractions and doping are presented. The absorption in the films with low Al fraction (1%) shows little variation from comparable GaAs films while for 20% Al, the absorption is reduced. The spectral results on a device with 12% Al emitters and 11% Al barriers have shown a response of 0.6 A/W at 30 lm with D* = 3 · 10 Jones measured at 5 K. The low responsivity is due to the reduced number (3) of emitters in the test device, and when scaled for the number of emitters this is comparable to results obtained from GaAs/AlGaAs HEIWIP detectors. Based on these results, a design for a 300 lm detector is presented and potential difficulties in growth and fabrication such as dopant migration are discussed. 2005 Elsevier B.V. All rights reserved. PACS: 85.60.Gz; 78.66.Fd; 78.67.Pt