DETECTION OF INFRARED RADIATION WITHIN THE FORBIDEN GAP USING QWIPS BASED ON III-V SEMICONDUCTORS

Lesslie Guerra ^1,2 Germano Penello ^2,3 Luciana Pinto ^1,2 Renato Mourão ^2,4 Roberto Jakomin ^2,5 Mauricio Pires ^2,4 Marcos Degani ^2,6 Marcelo Maialle ^2,6 Patricia Souza ^1,2

¹LabSem, Pontifícia Universidade Católica do Rio de Janeiro
²DISSE, INCT de Nanodispositivos Semicondutores
³Departamento de Eletrônica e Telecomunicações, Universidade do Estado do Rio de Janeiro
⁴Instituto de Física, Universidade Federal do Rio de Janeiro
⁵Campus de Xerém, Universidade Federal do Rio de Janeiro
⁶Faculdade de Ciências Aplicadas, Universidade Estadual de São Paulo

III-V semiconductors are extensively investigated for the fabrication of quantum well infrared photodetectors (QWIP) due to the mature state of their epitaxial growth, which can routinely provide extremely homogeneous quantum well (QW) structures.

The infrared wavelength operation range for these devices is very broad and, in principle, not limited for long wavelengths, the limitation being mostly for short wavelengths. The minimum operation wavelength in QWIPs based on intrinsic intraband transitions is limited by the bandoffsets of the heterostructures, in general between 400 and 500 meV for III-V semiconductors, corresponding to 3.0 to 2.5 μm. On the other hand, for wavelengths shorter than 1.7 μm band to band transitions are easily employed. Therefore, the energy range between 1.7 μm (730 meV) and the bandoffset cannot be reached either by band to band or intraband transitions in III-V semiconductors, giving rise to sort of a “forbidden gap”. This energy range is particularly important for carbon monoxide detection [1, 2] and for satellite imaging in the band 7 of the short wavelength infrared, suitable for environmental monitoring since it is the best range for vegetation and hydrothermal inspection [3].

In this work we present for the first time specially designed InGaAs/InAlAs QWIPs which can detect radiation within this “unreachable” range with an optical transition where the photon absorption occurs between the ground state of a QW and a localized excited state in the continuum. Photon energies equal to 587 meV and 523 meV, larger than the bandoffset, were detected. Small changes in the thicknesses of the different layers allow tuning of the operation wavelength.

[1] C. Nicolas, A. N. Baranov, Y. Cuminal, Y. Rouillard and C. Alibert, Applied Optics 37, 7906, 1998.

[2] J. Kirby and R. K. Hanson, Applied Physics B 69, 505, 1999.

[3] See www.landsat.usgs.gov or www.landsat.gsfc.nasa.gov