Photoluminescence (PL) Techniques
Introduces the photoluminescence (PL) technique. This includes the layout of homebuilt PL setups and their methodology, including relevant parameters or the “information depth.” Most importantly, the diversity of the observed PL lines and bands is describ
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Photoluminescence (PL) Techniques
Abstract Introduces the photoluminescence (PL) technique. This includes the layout of homebuilt PL setups and their methodology, including relevant parameters or the “information depth.” Most importantly, the diversity of the observed PL lines and bands is described systematically and their microscopic nature is addressed. Steady-state and transient PL as well as related techniques, such as PL-excitation spectroscopy, are explained, and the results that are to be expected are discussed. This also includes PL mapping and PL imaging approaches. Case studies and guidelines on how to analyze complex structures complete the chapter.
4.1
Introduction
At first glance, the PL spectrum from a given semiconductor material or structure can be expected to represent the spectrum of spontaneous interband emission. This spectrum is created by the recombination of non-equilibrium carriers, which are generated by the absorption of photons, which are typically provided by an excitation laser source. The optical excitation led to the naming ‘PL’. According to Chap. 1, see (1.73), virtually a one-to-one correspondence to the absorption spectrum is expected. In a real-world semiconductor, however, this straight link is disturbed by many-particle effects and extrinsic effects such as the presence of surfaces, defects, disorder, carrier localization, etc. In practice, a PL spectrum includes mostly information that complements what one can obtain from absorption measurements. Therefore, PL and absorption spectroscopy can be considered as completely independent analytical tools. The spectral range, in which both types of measurements provide important and complementary information, is often the same, namely the range around the fundamental energy gap (Eg). Therefore, typical PL spectra cover the spectral range around Eg, this type of PL is often called edge emission. This term points to the interband absorption edge, a major resonance of any semiconductor’s interaction with electromagnetic radiation. Sometimes, PL can be detected at higher or lower photon energies than Eg as well. These types of PL will be addressed later in this chapter. © Springer International Publishing Switzerland 2016 J. Jimenez and J.W. Tomm, Spectroscopic Analysis of Optoelectronic Semiconductors, Springer Series in Optical Sciences 202, DOI 10.1007/978-3-319-42349-4_4
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4 Photoluminescence (PL) Techniques
While sensitive experimental setups allow for monitoring PL spectra from almost all semiconductor materials, in direct semiconductors PL spectroscopy is expected to provide richest information. Thus, we will focus our following considerations to direct materials. These are mainly the III-V compounds such as GaAs, InP, GaN, and II-VI materials such as ZnS, CdTe, ZnO. But there are many other materials, among them ternary and quarternary mixed crystal systems consisting of the binaries mentioned above, such as Ga1-xAlxAs or InxGayAl1-x-yP. Since Si is the most important semiconductor overall, we will address the PL-sp
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