M.Sc Thesis

M.Sc StudentDror Ben
SubjectIntersubband Infrared Optoelectronic Devices in
Gallium-Nitride on Silicon
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROF. Meir Orenstein


III-Nitrides such GaN, AlN are semiconductors with wide band gap of 3.54 and 6.28 eV, respectively. By design of nanometer layers structure and due to the conduction band offset, quantum wells (QWs) are created. Due to quantization in the QW subbands are created. An optical transition between subbands is called an intersubband transitions (ISBT). The conduction band offset between AlN and GaN is 1.85 eV which allows ISBT in the entire spectral range from near infrared (IR) to THz radiation. ISBT in GaN are naturally very fast thanks to the interaction with longitudinal-optic (LO) phonons whose energy is 92 meV. Typical relaxation times range from tens to several hundreds of femto-seconds. In addition, direct epitaxial growth of GaN based electronic devices on Silicon is an established, mature and proven technology. Combining Silicon compatibility with ISBT optoelectronic devices allows growth of IR detectors directly on Silicon and their fabrication in a CMOS compatible process. Such devices will operate in a broad spectral range, will be ultra-fast, reliable and at low cost. The demand for mass-production of low-cost IR detectors is on the rise in realms such as driver-assisting systems, autonomous cars, optical communications, process control and security.

This research focuses on two types of ISBT detectors in GaN: the first is a photovoltaic quantum well infrared photodetector grown on sapphire substrate. This is the first detector of its type in the GaN material system. Several detectors were fabricated and studied, their optical and electrical characteristics are presented and discussed in the thesis. The central wavelength of the detectors is 2.3 and 2.5 μm, depends on the specific model concerned. The responsivity and detectivity of the detectors was measured at room temperature, the zero bias responsivity at 45 degrees front illumination is 88 μA/W and the detectivity is 1.5 ? 106 Jones. The devices resistance and their spectral photo-signal were measured in 18 - 300 K temperature range.

The second detector that was studied is a quantum cascade detector grown epitaxially directly on Silicon. This mid-IR detector, which is the first ISBT detector grown epitaxially on Si was, is a technological breakthrough which opens a door to optoelectronic IR devices integrated with CMOS Si read out circuits. The central wavelength of the detector is 4.5 μm, the responsivity at 18 K is 44 μA/W and the detectivity is 2 ? 108 Jones. Optical measurements of absorbance in a bare polished sample along with the spectral response of the detector in temperatures of 18 - 150 K are presented and discussed, in addition dark current and differential resistance in temperatures of 18 - 300 K are measured and discussed. The differential resistance at zero bias is analyzed by a model which assumes dominant conduction mechanism of LO-phonon assisted tunneling and the source of the measured resistance is discussed. Finally, a plasmonic metal hole array is demonstrated which allows operation of the detector in a normal incident illumination, in contrast to a bare detector which must be illuminated in a tilted illumination.