Half-cavity structures in the infra-red
Our half-cavity photonic structure - nitride-based DBR - consists of alternating layers GaN and AlxGa1−xN. The advantage in using this type of DBRs is that the active layer, microcavity or light emitting elements, e.g. a quantum well or a quantum dot can be deposited in the same process used to deposit the layers for the DBR. This significantly simplifies the fabrication process of devices.
An optically ative layer emdedded in an optical cavity is GaN:(Mn, Mg). Co-doping with Mn and Mg with the concentration of both less than 1% results in the formation of robust cation complexes Mn-Mgk, responsible for a broad infra-red emission in the infra-red that covers two telecommunication windows, i.e. at 1.33 µm and 1.55 µm [1-2].
Recently, we have done an extensive work on deisgn, fabrication and testing half-cavity DBR structures, where GaN:(Mn,Mg) layer is deposited on top of the DBR structure. The center of a DBR stop-band is designed to be at 1200 nm, where a maximum of IR emission from Mn-Mgk complexes is observed. The maximum reflectivity that we have reached so far in the fully strained crystalline DBR structures is 62%, for 20 DBR pairs as can be seen in Fig. 1. In order to increase a crystal quality, we add < 1% of Mn in AlGaN layers . Photoluminescence measurements up to the room temperature confirm the enhamcement by a factor of five of the emission intensity from Mn-Mgk complexes in a GaN:(Mn,Mg) layer grown on the DBR structure shown in the Fig. 2 [4, 5].
- Figure 1: Transmission electron miscropy image of a DBR structure and a (0002) reciprocal space map with three peaks corresponding to 1 - GaN layers in DBR, 2 - AlGaN:Mn buffer and 3 - AlGaN:Mn layers in DBR .
- Figure 2: (a) Measured and calculated reflectivity spetra of a sample with 20 Bragg pairs. (b) Low temperature photoluminescence measurements of a sample with an active layer GaN:(Mn,Mg) deposited directly on a buffer and on a 20-folded DBR structure. An intensity enhancement by a factor of five is observed .