Źródła światła widzialnego następnej generacji wykorzystujące kryształy fotoniczne

The ultimate goal of the planned effort within the project is to fill in the gap in III-nitride emitters and establish the path towards photonic crystal (PhC) surface-emitting lasers by applying novel approach based on tunnel junction (TJ) heterostructures. What characterizes PhC-SEL is the use of two-dimensional (2D) PhC to form the planar cavity. The main issue related with this devices is a seamless integration of PhC with the LD heterostructure that consists of an active region sandwiched between p- and n-type cladding layers. For III-nitrides this integration is held back by two factors: (1) short emission wavelength of the device, which requires sophisticated electron-beam lithography for uniform PhC fabrication, and (2) problematic p-type doping in nitrides that imposes strict constrains on the placement of p-type layers on the very top of the heterostructure and causes high resistivity in case of p-type regrowth. While the first factor, as it was shown by many groups, can be addressed by proper processing optimization to obtain very reproducible, homogeneous 2D grating, the latter is intrinsically related with III-nitride material system. Here we propose to address the challenges related to the low p-type conductivity by the use of TJs to ease the PhC integration into the III-nitride SEL. TJ is a heavily doped p-n junction that can be placed on top of an optoelectronic device to change the p- to n-type conductivity and limit negative effects associated with p-doped layers. We have proven that such structures can be successfully grown at Institute of High Pressure Physics Polish Academy of Sciences (IHPP PAS) using plasma-assisted molecular beam epitaxy (PAMBE). We have also shown that conductivity offered by TJ allows for the construction of edge-emitting LD and vertical stacking of multiple LDs. Furthermore, we showed that TJ can also be used to form the so-called bottom-TJ laser diode structures. For bottom-TJ heterostructure the sequence of p- and n-type layers in the device is inverted leading the termination of the structure with the n-type material. Such structure offers unmatchable freedom in surface functionalization since the material is highly conductive and allows for further regrowth after patterning. First, we will investigate the impact of the GaN etching pattern on the photonic band structure in visible wavelengths. 2D numerical simulations will be used to identify PhC patterns that affect light propagation in the crystal. Test PhCs will be processed in bulk GaN substrates using electron-beam lithography. Second, we will study the GaN re-growth mechanism that would allow for reproducible and uniform PhC overgrowth. This step is necessary to increase the distance between PhC and crystal surface that will increase also the coupling of cavity with emitter underneath. Third, we will combine the bottom-TJ LED with PhC to present the enhancement of the radiative lifetime and change in the emission pattern. Exceptionally high cryogenic operation of the bottom-TJ comparing to standard LED will further help in observing the Purcell effect. Thin-film LEDs and membranes will be presented utilizing the electrochemical etching of the heavily n-type doped layer underneath. Fourth, we will obtain the photonic crystal surface emitting laser. Optical mode and heat distribution in the structure will be numerically simulated. Bottom cladding layer that would allow for good light confinement and easy heat dissipation will be optimized. Advantages of the PAMBE growth and the bottom-TJ design will be used to tackle the main challenges standing in front of III-nitride SELs. We predict that the use of bottom-TJ configuration will allow for a straight forward integration of III-nitride emitters with PhC and allow for the construction of high-power, narrow linewidth, high quality optical beam SELs operating at low current densities.