Optical storage in erbium-doped gallium nitride using focused ion beam nanofabrication

In this research, we propose a concept for a high-density, page-oriented data storage using optical upconversion emission from erbium doped gallium nitride (GaN:Er). This alternative storage design is based on nonlinear optical process of rare earth (RE) doped in wide bandgap semiconductor host. Data is recorded with focused ion beam (FIB) write technology and retried as amplitude modulated signal by detecting the incoherent upconversion emission. Writing process with FIB could be implemented with either ion implantation or ion milling approach.; With ion implantation approach, Er ions were implanted by FIB into undoped GaN thin film grown on sapphire or silicone (Si) substrates. Thermal annealing process was applied next to activate the optical properties of implanted Er ions. Information stored as data bits consists of patterns of implanted locations as logic ‘1’ and unimplanted locations as logic ‘0’. The photon upconversion process in Er ions is utilized to read the stored information. This process makes use of infrared (IR) lasers (840 nm and 1 μm) to excite visible emission (522 and 546 nm). Patterns as small as 0.5 μm were implanted and read. Volumetric optical memory based on GaN:Er semiconductors could in theory approach storage capacity of 1012 bits/cm 3.; With ion milling approach, sub-micron patterns were micro-machined on MBE grown in-situ doped GaN:Er film on Si substrate. Data retrieval is accompanied by upconversion emission at 535 and 556 nm upon 1 μm IR laser stimulation. Regions where Er-doped GaN layer is completely removed (and do not emit) are defined as logic ‘0’, while regions that are not milled (and do emit) are defined as logic ‘1’. Data patterns with submicron bit size (or 100 Mbits/cm2 density) have been fabricated by FIB milling. Data written by this approach has a theoretical storage capacity approaching 10 Gbits/cm2.; Our implementation of this proposed optical storage architecture takes advantage of capabilities that is available in the Nanoelectronics Laboratory such as, non-optical recording technique with FIB implantation or milling, liquid alloy ion source fabrication, epitaxial growth of GaN films by molecular beam epitaxy, upconversion optical readout set-up, and visible to IR optical characterization.