Physics and technology of mid–infrared light emitting diodes

Abstract

There is increasing interest in mid-infrared (mid-IR) light emitting diodes which operate in the 2-5 µm spectral region. Efficient LEDs operating at the characteristic absorption wavelengths of target gases, such as CH 4 , CO 2 and CO, have great potential for the next generation of optical gas sensors. The fundamental difficulties associated with realizing suitable mid-IR LEDs at different wavelengths, with high continuous wave (CW) output power at room temperature, relate principally to quantum efficiency and optical extraction of the light. Each of these will be briefly considered. Some of the different device designs and techniques used for the suppression of non-radiative Auger recombination and the reduction of Shockley-Read-Hall centres are discussed. Liquid phase epitaxy (LPE) continues to hold a strong position in mid-IR LED technology and many of the best LEDs currently available have been fabricated using this technique. In this respect, the LPE growth of associated InAs(Sb)-based epitaxial structures and their purification is briefly reported. An overview of the 'state of the art' is also given with respect to the application of mid-IR LEDs in practical gas sensors.

The effect of pressure on the radiative efficiency of InAs based light emitting diodes

“…This makes the An term in Eq. (1) insignificant at room temperature (other experiments have also supported this conclusion [1], [6]). Further, the capture cross section for recombination through defects is almost independent of pressure, allowing the An term to be neglected in our analysis.…”

“…The main target of such devices is to provide sufficient output power for the development of selective, highly efficient optical gas sensors capable of identifying target gases such as CH 4 , CO 2 and CO. The alloy systems based on InAs substrate are promising materials for the fabrication of midinfrared light sources for such applications [1]. The principal challenges for efficient room temperature operation are to reduce non-radiative mechanisms such as Auger recombination processes [2 -4] .…”

Raman scattering in InAsxSbyP1−x−y alloys grown by gas source MBE

“…Similarly, although the InAsSbP/InAs interface is thought to be type II [25], in our case the layers are sufficiently thick so that the substrate plays no part in the Raman spectroscopy. However, the peaks can become broadened due to the stresses induced from lattice mismatch.…”

Effect of high carrier injection on the performance of a mid-infrared DH-LED

“…But its room temperature continuous operation and high power output is limited by non-radiative recombination such as Shockley-Read-Hall (SRH) and Auger recombination process, which are usually dominating recombination mechanisms for narrow bandgap material system especially at high injection level. A number of mid-infrared Light Emitting Diodes have been fabricated and studied in the recent past [1]- [3]. In the present paper we have developed a generic model of a double heterostructure LED and applied our model to the P + -InAs 0.48 Sb 0.22 P 0.30 / n 0 -InAs 0.89 Sb 0.11 / N --InAs 0.48 Sb 0.22 P 0.30 DH-LED structure proposed for the 3-5 m spectral region by Gao et al [4].…”