Intersubband transitions in III-V semiconductors for novel infrared optoelectronic devices

Mohammed Imrul Hossain, Purdue University

Abstract

Intersubband transitions (ISBTs) in the conduction band (CB) of semiconductor multiple quantum wells (QW) have led to devices, like quantum-well infrared photodetectors and quantum cascade lasers (QCL). Due to the complexities related to the valence band (VB), hole ISBTs have not been explored as intensively as their electronic counterparts. Absorption and photoluminescence due to ISBT in the VB have been reported for p-type Si-SiGe QWs but this material system suffers from significant challenges associated with the built-in strain of these lattice mismatched materials. The GaAs/AlGaAs material system is virtually strain-free and quite mature. We are investigating the properties of bound-to-bound inter-valence subband transitions in GaAs QWs with high Al composition barriers for mid-infrared emitters. Hole ISBTs are interesting because the polarization of the light emitted in heavy-to-light hole transitions is not restricted to the perpendicular of the quantum wells (unlike electron ISBTs in the CB due to selection rules), therefore surface emitting QCLs and ultimately vertical-cavity surface emitting devices are possible using these transitions. Moreover the valence-band offset for pure GaAs and AlAs is comparable with the conduction-band offset in the traditional InGaAs/InAlAs lattice matched to InP system. Very recently we have observed strong heavy to light hole absorption and heavy to heavy hole electroluminescence from ridge waveguide structures in the mid infra-red range. We are also investigating dual wavelength mid infra-red QCLs in the InGaAs/InAlAs system lattice matched to InP. This device may be useful in applications like differential absorption lidar where light has to be evaluated and compared at two different frequencies for environmental sensing application. Most approaches to multi-wavelength QCL operation involve the use of heterogeneous cascades. Our design involves a single type of active region, emitting at two widely different wavelengths in the mid-infrared range. Our results provide insights in the detail charge transport and optical properties of this design concept. We are also investigating the possibility of inversionless lasing of this type of dual wavelength. My research encompasses the fabrication and processing of nanoscale semiconductor devices on high quality MBE grown wafers from our collaborators. The fabrication includes e-beam evaporation, photolithography, dry and wet etching, rapid thermal annealing, step height analysis, plasma etching, PECVD and also mask designing. The characterization and analysis of the optoelectronic devices is performed through FTIR (Fourier transform infra-red) spectroscopy. The material systems I have directly worked on are Silicon, GaAs/AlGaAs and InGaAs/InAlAs lattice matched to InP. Very recently I have also done some device processing in the InAlN/GaN material system.

Degree

Ph.D.

Advisors

Manfra, Purdue University.

Subject Area

Electrical engineering|Condensed matter physics|Nanotechnology|Materials science

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