Recent development of UV-B laser diodes

Abstract

This review paper describes the history of development, current issues, and future expectations of UV-B laser diodes, which are expected to be adopted in various applications such as microfabrication and biotechnology in the near future. In order to achieve room temperature operation of this device, there were several challenges are remained, including the development of a crystal growth technique of high crystalline quality AlGaN that enables a laser oscillation with a low excitation carrier density, and the development of a semiconductor layer structure that simultaneously formation of a desirable optical cavity and injection of high density carriers (operation of high current density) to active layer allowing for laser oscillation. These challenges and the technologies that have overcome them are reviewed. Current status of the device characteristics and future challenges are also discussed.

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

“…Second, there is a large gap between the transparency threshold and the minimum threshold current density, sometimes approaching an order of magnitude difference. This gap has a distinct correlation with threading dislocation densities typical for AlGaN alloys, which were shown in Figure 1 of the review reported in [ 24 ]. This correlation reveals a very critical effect of threading dislocation density (TDD) on the threshold current density of DUV-LDs, which was further confirmed by direct measurements reported in [ 25 , 28 , 29 , 30 ], see Figure 2 a (TDD for the lowest threshold current density shown in this figure was not reported in [ 25 ], but we estimated TDD in the range of ~10 6 –10 7 cm −2 ).…”

“… Experimental threshold current densities of UV laser diodes fabricated on various substrates (symbols) vs. oscillation wavelength [ 24 , 25 , 26 ]. The grey line is an approximation for the minimum threshold current density drawn as a guide to the eye.…”

“…Figure 1 summarizes reported experimental threshold current densities (symbols) of UV laser diodes for different emission wavelengths. The data were obtained from [ 24 , 25 , 26 ]. Detailed description of the results by various research groups is given in [ 24 ].…”

“…The data were obtained from [ 24 , 25 , 26 ]. Detailed description of the results by various research groups is given in [ 24 ]. The approximation for the minimum threshold current density is shown in Figure 1 as a guide to the eye by the grey curve.…”

Review of Fluorescence Spectroscopy in Environmental Quality Applications

“…Light is emitted by flowing electrical current through the semiconductor due to the energy gap in the diode’s junction. They are compact lasers that emit wavelengths typically from visible to IR, but recently there are devices emitting in the UV region [ 9 ]. Their output has a wide range of power from low to moderate.…”