Exciton localization behaviour in different well width undoped GaN/Al0.07Ga0.93N nanostructures

Abstract

We report results from optical spectroscopy such as photoluminescence (PL) and time resolved photo-luminescence (TRPL) techniques from different well width MOCVD grown GaN/Al0.07Ga0.93N MQW samples. There is evidence of localization at low temperature in all samples. The decay time of all samples becomes non-exponential when the detection energy is increased with respect to the peak of the emission. Localization of carriers (excitons) is demonstrated by the “S-shape” dependences of the PL peak energies on the temperature. The time-resolved PL spectra of the 3-nm well multi quantum wells reveal that the spectral peak position shifts toward lower energies as the decay time increases and becomes red-shifted at longer decay times. There is a gradient in the PL decay time across the emission peak profile, so that the PL process at low temperatures is a free electron-localized hole transition.

Impact of alloy fluctuations and Coulomb effects on the electronic and optical properties of c-plane GaN/AlGaN quantum wells

“…As the temperature keeps increasing, the red-shifting PL peak energy reflects the phonon-mediated energy gap shrinkage becoming the dominant effect. The observed “S-shape” temperature dependence of the PL peak position in our GaN/AlGaN MQWs is consistent with the results obtained by other groups on such heterostructures 45,46 .

Figure 4Peak PL energy as a function of temperature for GaN/AlGaN MQWs with well widths of nm (Sample A) and nm (Sample B). The filled circles show the raw data, and the triangles show the data with the band gap temperature dependence removed using the two-parameter Varshni expression.

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“…As the decays are non-exponential, we have determined the decay time by the time taken for the photon count to decrease by a factor of 1/e. The 1/e decay times for Sample B show that varies across the spectrum, comparable to the recombination energy dependence of the radiative lifetime reported in both InGaN/GaN 13,48–50 and GaN/AlGaN QWs 46,51 and attributed to carrier localization. Here, the decay times increase from 14 ns to 40 ns when the detection photon energy decreases from 3.30 eV to 3.27 eV.…”

GaN nanorods grown on Si (111) substrates and exciton localization

“…Furthermore, it has been claimed that this localization gives rise to the high quantum efficiency commonly found in III-nitrides by preventing the carriers from reaching the dislocation level (which acts as many non-radiative recombination centers) [3,4]. These localizations are caused by alloy fluctuations in ternary semiconductors such as AlGaN [5,6] and InGaN [7,8] and in multi-quantum well structures such as AlGaN/GaN [9] and InGaN/GaN [10]. In binary systems such as GaN nanorods, clear identification of exciton localization with an appropriate analysis has rarely been reported.…”

Tunable Localized Charge Transfer Excitons in Nanoplatelet–2D Chalcogenide van der Waals Heterostructures

“…Therefore, spatial localization of the CTXs can be verified via excitation power dependent TEPL response since emission rate is limited by the density of localized states. 37,38 Hence, to confirm the spatial localization characteristic, we perform excitation power dependent TEPL measurements. Figure 2f displays a log−log plot of PL intensity of all excitonic species as a function of excitation power.…”

“…Since CT excitons are formed at the interface between NPL and MoSe 2 , the spatial extent of this exciton should be localized within the in-plane dimensions of the NPL, which typically range from 10–40 nm (see Supporting Information, Section I). Therefore, spatial localization of the CTXs can be verified via excitation power dependent TEPL response since emission rate is limited by the density of localized states. , Hence, to confirm the spatial localization characteristic, we perform excitation power dependent TEPL measurements. Figure f displays a log–log plot of PL intensity of all excitonic species as a function of excitation power.…”