A. A. Erchak¹, D. J. Ripin², S. Fan², G. S. Petrich³, J. D. Joannopoulos², L. A. Kolodziejski³, and E. P. Ippen^2,3

¹Department of Materials Science and Engineering

²Department of Physics

³Department of Computer Science and Electrical Engineering, Research Laboratory of Electronics, Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307

A two-dimensional photonic crystal is used to eliminate planar waveguiding in a high dielectric light-emitting diode and enhance the coupling of spontaneous emission into free space modes[S. Fan et al, Phys. Rev. Lett. 78, 3294 (1997)]. The photonic crystal consists of a hexagonal lattice of holes etched into the top cladding layer of an InGaP/InGaAs quantum well structure emitting at l=980 nm. To eliminate nonradiative surface recombination, the holes are not etched through the active region (figure 1a), yet are deep enough to open a photonic band gap and eliminate planar waveguiding. A 6-fold increase of surface normal photoluminescence is observed and attributed to the presence of the photonic crystal (figure 1b).

In the poster presentation, the two-dimensional photonic band gap light-emitting diode (2D PBG LED) design, fabrication, and optical characterization will be described. The photonic crystal is designed such that the emission wavelength lies inside the photonic band gap contrary to previous attempts at enhancing light extraction [M. Boroditsky et al, Appl. Phys. Lett. 75, 1036 (1999)]. The fabrication of the 2D PBG LED utilizes gas source molecular beam epitaxy, direct-write electron beam lithography, reactive-ion etching, and oxidation processes. Room temperature PL spectroscopy is performed with a cw 810 nm Ti:Al2O3 pump laser, focused to a 6 mm spot size on the sample.

Fig. 1a. Cross-sectional view of 2-D PBG LED structure. The hole depth is only 120 nm while the thickness of the top InGaP cladding layer is 158 nm. The holes do not penetrate the InGaAs quantum well to avoid surface recombination. Fig. 1b. Spatially resolved photoluminescence (PL) is taken with the 2D PBG LED sample translated with respect to the pump beam. The position of the pump beam during each line scan is shown by the schematics below each trace. The bottom trace is collected at 890 nm, and is PL from the GaAs substrate. The middle trace, collected at 980 nm, is PL from the quantum well. The top trace is PL from a line scan passing through one mesa without a PBG, and four mesas with PBGs