M.Sc Thesis

M.Sc StudentYokev Idan
SubjectToward GaN on Si based Monolithic Integrated
Inter-Subband IR Optoelectronics
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROFESSOR EMERITUS Gad Bahir
PROF. Meir Orenstein
Full Thesis textFull thesis text - English Version


We report for the first time a CMOS process-compatible intersubband transition (ISBT) infrared (IR) detector that is epitaxially selectively grown on Silicon (Si) wafers. Integrated, CMOS-compatible IR detectors are very desirable since they will revolutionize applications such as autonomous vehicles and defense. Currently, fabrication of IR detectors for imaging requires separate materials for the integrated circuits (ICs) for driving and signal processing and the actual detecting pixel arrays.

This significantly increases the complexity of the system and hinders the wide adoption of IR sensing systems.

Using III-Nitrides (III-Ns) such as Gallium-Nitride (GaN) and Aluminum-Nitride

(AlN), one can design a Quantum Cascade Detector (QCD)-based IR sensor with an

absorption anywhere in the spectral range from Near IR (NIR) wavelengths to THz radiation.

Among the III-V material systems, only the GaN system is a mature and proven

technology for epitaxial growth on Si and for standard CMOS-compatible fabrication.

This research continues previous efforts, which resulted in a III-N-based QCD grown

on Si for Mid-IR (MIR) wavelength range. Our goal was to expand the material system capabilities to fabricate a fully integrated IR detector in silicon. Foremost, we studied the optimization of the CMOS compatible, Selective Area Growth (SAG) process for a viable MBE GaN QCD growth, which was done at NTU. To test the GaN QCD SAG process a Si (111) wafer, with a thermally grown oxide layer on which various SAG windows were etched, was sent to NTU for GaN-QCD growth. The process development stages will be discussed and analyzed.

Several SAG grown QCDs were fabricated and assembled, the photo-signal was

measured using a 45º incident light configuration, at temperatures in the range of 20 - 100 K, the signal degraded below the noise level at higher temperatures. The devices showed peak absorbance at 4.6-4.7 µm wavelength, the responsivities were measured at 20 K and detectivities were derived assuming dominant Johnson noise. At 20 K the responsivity was 44.4 µA/W and detectivity 1.45-1.66?10^7 Jones.

Concurrently, comparative measurements of MOS devices and Sentaurus Process

simulations were performed and the results show that the QCD growth cycle has a small effect on capacitor characteristics and no effect on doping profile.

A second device, a QCD designed for the NIR (peak wavelength 1.53 µm), based on the same material system, was grown on Si, fabricated, and studied. The photo-signal was measured using a 45º incident light configuration, at temperatures in the range of 300-20 K, with the signal degrading at lower temperatures. At 300 K the responsivity was 0.9 µA/W and detectivity was 2 ? 10^5 Jones.

Finally, a plasmonic metal hole array (MHA), which allows operation of the detector

in normal incidence, was designed for a QCD MIR detector. Using Lumerical FDTD

simulation, an accurate layer description was required, down to the Si substrate, to optimize the MHA parameters. The resulting device exhibited a responsivity of 9.5 µA/W under normal incident illumination; its detectivity was 2.3?10^8 Jones at 19 K. Further improvements in responsivity by etching the silicon substrate were attempted and will be discussed.