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Planar ultraviolet radiation detectors based on GaN grown on silicon substrate with novel double oxide buffer layer

Final Report Summary - GANOXSI (Planar ultraviolet radiation detectors based on GaN grown on silicon substrate with novel double oxide buffer layer)

The main research objectives of the “GaNOxSi” project were a development of the growth technology of GaN layer on silicon substrate with application of novel double oxide buffer layers as well as design of device technology and construction of ultraviolet planar detectors.
Detection and measurement of light radiation in ultraviolet range have great importance in the areas of clean coal technologies (e.g. combustion engine control) and security of citizens (e.g. control units for drinking water disinfection systems, monitoring of sun UV radiation influence on biological systems, rocket missile detection). Using GaN and its alloy with Al for detectors fabrication gives the very important advantage of natural solar blindness of spectral characteristics and to tune furthermore the spectral detector properties as a function of alloy composition; in addition, the ability to operate in harsh environmental conditions is a further noteworthy advantage of AlGaN heterosystems.
Application of silicon substrates for GaN epitaxy increases the yield and economical profit of mass production of GaN based devices. Simultaneously, it requires usage of advanced materials technology to reduce the detrimental effects of lattice and thermal expansion coefficient differences between Si and GaN on epitaxial layer quality. In our approach, also utilized in this project, we have applied a step-graded, double oxide (Sc2O3/Y2O3) buffer layer.
For fabrication of GaN/Sc2O3/Y2O3/Si(111) heterostructures a multichamber Molecular Beam Epitaxy (MBE) system was used. The quality of grown structures was measured by: Reflection High Energy Electron Diffraction (RHEED), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and Raman spectroscopy. As a result thick, single crystalline wurtzite GaN(0001) layers on Si substrate were grown with structural and optical quality sufficient for test detector structures elaboration.
The silicon/oxide system for GaN epitaxy offers the additional advantage of forming distributed Bragg reflector (DBR) layers at the GaN – Si boundary, a device structure that increases the detector photoresponsivity. Utilizing this idea, the heterostructure consisting of GaN / Sc2O3 / DBR (3.5 x (Y2O3 / Si)) layers on Si(111), with DBR designed for UV wavelength operation were fabricated (figure)
GaN on Si and GaN on DBR / Si samples were further processed to fabricate MSM UV photo-detector test structures. To obtain a Schottky contact of a metal-semiconductor-metal (MSM) detector a various metal layers was deposited by electron beam (platinum, iridium) and resistive (gold) evaporation. Sc2O3 oxide leakage current suppression layers for (metal-oxide-semiconductor) M-O-S contacts were also deposited using the MBE oxide process. After deposition, the contacts were thermally formed by RTA (rapid thermal annealing) processes in nitrogen atmosphere Metal shadow masks were used to obtain interdigitated MSM detector electrodes. The current-voltage-temperature characteristics of M-S and M-O-S contacts to GaN were measured to calculate Schottky contact parameters. The photoresponse spectral characteristic of detectors, measured with application of developed during project optical system, presented desirable UV photosensivity with maximum response observed around ~360 nm which well coincides with the expected GaN band gap values.
The most important results of the project
- Elaboration of the fabrication technology of ultraviolet metal-semiconductor-metal detector based on gallium nitride on silicon via buffer oxides layer with application of M-O-S contacts
- Elaboration of GaN on Si (111) layers with embedded 3.5 pairs of Y2O3/Si distributed Bragg reflectors
- Obtaining 100% increase of detector photoresponse in UV light region in structures with application of DBR