An official website of the United States government
Abstract Realizing stimulated emission from defects in 2D‐layered semiconductors has the potential to enhance the sensitivity of characterizing their defects. However, stimulated emission from defects in layered materials presents a different set of challenges in carrier lifetime and energy level design and is not achieved so far. Here, photoluminescence (PL) spectroscopy, Raman spectroscopy, and first‐principles theory are combined to reveal an anomalous PL intensity–temperature relation and strong polarization effects at a defect emission peak in annealed multilayer MoS2, suggesting defect‐based stimulated emission. The emergence of stimulated emission behavior is also controllable (by temperature) and reversible. The observed stimulated emission behavior is supported by a three‐level system involving two defect levels from chalcogen vacancies and a pump level from the conduction band edge. First‐principles calculations show that the special indirect gap that enables stimulated emission is not native to pristine bulk MoS2and only emerges under thermal strain.
more »
« less
Mechanisms of Thermal Quenching of Defect‐Related Luminescence in Semiconductors
The intensity of defect‐related photoluminescence (PL) in semiconductors changes with temperature, and it usually decreases exponentially above some critical temperature, a process called the PL quenching. Herein, main mechanisms of PL quenching are reviewed. Most examples are given for defects in GaN as the most studied modern semiconductor, which has important applications in technology. Peculiarities of defect‐related PL in I–VII, II–VI, and III–V compounds are also reviewed. Three basic mechanisms of PL quenching are distinguished. Most examples of PL quenching can be explained by the Schön–Klasens mechanism, whereas very few or even no confirmed cases can be found in support of the Seitz–Mott mechanism. Third mechanism, the abrupt and tunable quenching, is common for high‐resistivity semiconductors. Temperature dependence of capture coefficients and a number of other reasons may affect the temperature dependence of PL intensity. The “negative quenching” or a significant rise in PL intensity with temperature is explained by a competition between recombination channels for minority carriers.
more »
« less
- Award ID(s):
- 1904861
- PAR ID:
- 10163787
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- physica status solidi (a)
- Volume:
- 218
- Issue:
- 1
- ISSN:
- 1862-6300
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Photoluminescence (PL) spectroscopy has been used to study the defect levels in thin film copper indium diselenide (CuInSe2, CIS) which we are developing as the absorber layer for the bottom cell of a monolithically grown perovskite/CuInSe2 tandem solar cell. Temperature and laser power dependent PL measurements of thin film CIS for two different Cu/In ratios (0.66 and 0.80) have been performed. The CIS film with Cu/In = 0.80 shows a prominent donor-to-acceptor peak (DAP) involving a shallow acceptor of binding energy ~22 meV, with phonon replica at ~32 meV spacing. In contrast, PL measurement of CIS film for Cu/In = 0.66 taken at 20 K exhibited an asymmetric and broad PL spectrum with peaks at 0.845 eV and 0.787 eV. Laser intensity dependent PL revealed that the observed peaks 0.845 eV and 0.787 eV shift towards higher energy (aka j-shift) at ~11.7 meV/decade and ~ 8 meV/decade with increase in laser intensity respectively. The asymmetric and broad spectrum together with large j-shift suggests that the observed peaks at 0.845 eV and 0.787 eV were related to band to-tail (BT) and band-to-impurity (BI) transition, respectively. Such a band-tail-related transition originates from the potential fluctuation of defect states at low temperature. The appearance of band related transition in CIS film with Cu/In = 0.66 is the indicator of the presence of large number of charged defect states.more » « less
-
Abstract Single-photon defect emitters (SPEs), especially those with magnetically and optically addressable spin states, in technologically mature wide bandgap semiconductors are attractive for realizing integrated platforms for quantum applications. Broadening of the zero phonon line (ZPL) caused by dephasing in solid state SPEs limits the indistinguishability of the emitted photons. Dephasing also limits the use of defect states in quantum information processing, sensing, and metrology. In most defect emitters, such as those in SiC and diamond, interaction with low-energy acoustic phonons determines the temperature dependence of the dephasing rate and the resulting broadening of the ZPL with the temperature obeys a power law. GaN hosts bright and stable single-photon emitters in the 600–700 nm wavelength range with strong ZPLs even at room temperature. In this work, we study the temperature dependence of the ZPL spectra of GaN SPEs integrated with solid immersion lenses with the goal of understanding the relevant dephasing mechanisms. At temperatures below ~ 50 K, the ZPL lineshape is found to be Gaussian and the ZPL linewidth is temperature independent and dominated by spectral diffusion. Above ~ 50 K, the linewidth increases monotonically with the temperature and the lineshape evolves into a Lorentzian. Quite remarkably, the temperature dependence of the linewidth does not follow a power law. We propose a model in which dephasing caused by absorption/emission of optical phonons in an elastic Raman process determines the temperature dependence of the lineshape and the linewidth. Our model explains the temperature dependence of the ZPL linewidth and lineshape in the entire 10–270 K temperature range explored in this work. The ~ 19 meV optical phonon energy extracted by fitting the model to the data matches remarkably well the ~ 18 meV zone center energy of the lowest optical phonon band ($$E_{2}(low)$$ ) in GaN. Our work sheds light on the mechanisms responsible for linewidth broadening in GaN SPEs. Since a low energy optical phonon band ($$E_{2}(low)$$ ) is a feature of most group III–V nitrides with a wurtzite crystal structure, including hBN and AlN, we expect our proposed mechanism to play an important role in defect emitters in these materials as well.more » « less
-
Abstract Here, the observation of spin‐polarized emission for the Au25(SC8H9)18monolayer‐protected cluster (MPC) is reported. Variable‐temperature variable‐field magnetic circular photoluminescence (VTV‐MCPL) measurements are combined with VT‐PL spectroscopy to provide state‐resolved characterization of the transient electronic structure and spin‐polarized electron‐hole recombination dynamics of Au25(SC8H9)18. Through analysis of VTV‐MCPL measurements, a low energy (1.64 eV) emission peak is assigned to intraband relaxation between core‐metal‐localized superatom‐D to ‐P orbitals. Two higher energy interband components (1.78 eV, 1.94 eV) are assigned to relaxation from superatom‐D orbitals to states localized to the inorganic semirings. For both intraband superatom‐based or interband relaxation mechanisms, the extent of spin‐polarization, quantified as the degree of circular polarization (DOCP), is determined by state‐specific electron‐vibration coupling strengths and energy separations of bright and dark electronic fine‐structure levels. At low temperatures (<60 K), metal–metal superatom‐based intraband transitions dominate the global PL emission. At higher temperatures (>60 K), interband ligand‐based emission is dominant. In the low‐temperature PL regime, increased sample temperature results in larger global PL intensity. In the high‐temperature regime, increased temperature quenches interband radiative recombination. The relative intensity for each PL mechanism is discussed in terms of state‐specific electronic‐vibrational coupling strengths and related to the total angular momentum, quantified by Landég‐factors.more » « less
-
Band-to-band photoluminescence (PL) imaging is one of the experimental techniques widely used to assess non-radiative recombination rates at a fixed incident light intensity. Minority carrier lifetimes in semiconductors such as mc-Si are also affected by optical injection levels. These can be measured by transient photoconductance (TPC). In this paper, PL imaging of shunts and TPC lifetime results for incident intensities of up to 50 Suns are compared for multiple samples of mc-Si.more » « less
