Light sources for wavelengths >2 μm grown by MBE on InP using a strain relaxed buffer

Light emitting diodes (LEDs) and lasers operating in the 2 to 3 μm spectral region at room temperature are been demonstrated. The devices were fabricated from In_xGa_1-xAs/InAs_y P_1-y double heterostructures grown on n-type InP (100) substrates by molecular beam epitaxy. A strain relaxed buffer layer which incorporates composition reversals was used to reduce the threading dislocation density and to accommodate the large lattice mismatch (up to 2.7%) between the InP substrate and the device active region. Efficient electroluminescence emission at wavelengths between 2 and 3 μm was obtained from the LEDs at room temperature, while diode lasers exhibited coherent emission in the range 2-2.6 μm at temperatures up to 130 K. For one of the LEDs a characteristic absorption was readily observed at 2.7 μm in the diode electroluminescence emission spectrum, corresponding to strong water vapour absorption in the atmosphere. These devices could easily form the key component of an infrared gas sensor for water vapour detection and monitoring at 2.7 μm in a variety of different applications