Abstract
Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers.
Highlights
Since their invention in 1994 ͑Ref. 1͒ quantum cascadeQClasers have rapidly established themselves as tunable coherent sources in the mid-infraredmid-IRrange of the electromagnetic spectrum.2 Improvements since their first introduction include room temperature operation, THz emission, and fabrication in a wide variety of binary and ternary III–V heteroepitaxial semiconductor material systems
Since intersubband transitions are transverse magneticTMpolarizedi.e., the electric field is orthogonal to the layers, conventional QC lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration
FIG. 7. ͑a Completed device andbenlargement showing the photonic crystal area surrounded by a patterned nitride isolation and thick contact metal
Summary
Since their invention in 1994 ͑Ref. 1͒ quantum cascadeQClasers have rapidly established themselves as tunable coherent sources in the mid-infraredmid-IRrange of the electromagnetic spectrum. Improvements since their first introduction include room temperature operation, THz emission, and fabrication in a wide variety of binary and ternary III–V heteroepitaxial semiconductor material systems. The patterned e-beam resist is transferred to the underlying silicon oxide hard mask layer via reactive ion etching using CHF3 , typically 20– 40 min II. It proved critical to clean the polymeric buildup which occurs during the hard mask etching step to successfully transfer the PC pattern into the active QC layers. We introduced a very thin layer of Ti for sticking purposes, after testing the procedure on a surface–plasmon QC laser processed as a regular stripe In addition this thin cladding method aids in achieving a better current uniformity into the active area of the device. The stringent requirement for vertical holes in the active semiconductor etch is evident This deposition must provide the topside contact while preventing electrical shorting of the top contact to the substrate. Figure 7͑bshows the region where the thick bondable contact transitions to the thin top side contact after the complete process sequence
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