UV and deep-UV light emitting and laser diodes based on the III-Nitride material system (typically alloys of Al(Ga,In)N) have been the subject of intense interest due to the lack of semiconductor lasers at this wavelength. In recent years, there have been numerous demonstrations of light emitting diodes in this wavelength range. Success with producing laser diodes is more limited, with almost all reports based on optical pumping of the semiconductor with an even deeper UV excimer laser, obviously not a practical solution. Furthermore, all reports of both electrically pumped LEDs and LDs suffer from low output power and efficiency, especially as the wavelengths push deeper into the UV.
This invention proposes a method to overcome the key limitation of electrically pumped lasers based on AlN, AlGaN, or AlInGaN, namely the lack of suitable shallow donor and acceptor dopants. As the band gap of these materials increases (and the emission wavelength decreases), both electrons and holes require greater thermal energies in order to ionize. By using sub-band gap light of sufficient energy to excite electrons (holes) from the relatively deep donor (acceptor) levels in the n-type (p-type) layer, the conductivity of these layers can be effectively increases by many orders of magnitude and both electrons and holes can be injected into the quantum well of the device, resulting in light emission.
- Uses significantly less energy to create a UV/DUV photon than an excimer laser.
- UV/DUV laser diode could potentially be integrated on chip using an InGaN based layer.
- Using total internal reflection of whispering gallery mode can overcome the key shortcoming of low absorption coefficient of the dopants.
- The effective carrier lifetime of the excited electrons and holes in the p- and n-type layers can be designed to be longer than when using an above band gap laser.
- Compact, efficient laser diode sources for lithography and metrology, biotechnology and materials processing applications.
Current stage of technology development: TRL 2
LLNL has filed for patent protection on this invention.
US Patent Application No. 2023/0327400 Photoconductive Semiconductor Laser Diodes and LEDs published 10/12/2023