M.Sc Thesis


M.Sc StudentAlon Vardi
SubjectMaterial and Device Characterization of GaN/AlN Quantum
Dots
DepartmentDepartment of Electrical Engineering
Supervisors Professor Emeritus Bahir Gad
Full Professors Gershoni David


Abstract

Intraband transitions in GaN/AlN heterostructure offers grate prospect for optoelectronic devices such as emitters, modulators and detectors. The large difference between the band-gaps of GaN and AlN, mostly associated to the conduction band, makes it possible to implement quantum structures in which the confining barrier is exceptionally high (1.8 eV). Thus, discrete energy levels (or sub-bands) are formed, within which intraband transitions in the near IR region are attainable. One can design the dimensions of such structures to fit, in particular, intraband transitions in the telecommunication spectral region (1.3-1.55 micron). Since the band-gap of these materials is considerably large, it is predicted that intraband devices in this system will be able to operate at room temperatures with a low dark current (or low threshold). Different groups have shown intraband transition rates in the range of THz in GaN/AlGaN quantum structures. Therefore, a major effort is invested in attempting to fabricate optoelectronic devices in this material system.

In this work, we fabricated and characterized the first GaN/AlN Quantum Dot Infrared Photodetector (QDIP) based on intraband absorption and in-plane carrier transport. The detector operates at room temperature with peak responsivity of 8mA/W at 1.42 micron. The measured response is completely polarized in the growth direction. This response is associated with the transition S-Pz, from the dot ground state (S) to the first excited level with two nodes along the growth axis (Pz).

Using Infrared spectroscopy we were able to measure directly the transition S-Pz, and compare it to the photocurrent spectrum. We found that the photocurrent spectrum is slightly blueshifted with respect to the absorption. The blueshift is consistently larger for bigger dots, meaning that the bigger the dots are, the larger the blueshift is. Moreover, we found that with the rise of temperature, the blueshift between the absorption and the photocurrent grows, while the responsivity increases exponentially.

To account for these extraordinary phenomena we applied an eight band kp model to the structure which shows that these results can be well understood in terms of band alignment between the Pz level in the dots and the wetting layer ground state.