High quality ternary (InGaN) and quaternary (AlInGaN) alloys have attracted a great attention in the last 20 years due to the large progress in epitaxial growth techniques which has led to the demonstration of highly efficient optical devices and solar cells [1], high electron mobility transistors [2], and, recently, photo-electrochemical (PEC) devices for water splitting cells [3]. These alloys show a bandgap tunable with composition, covering the whole spectrum from the infrared (InN, Eg ∼ 0.7 eV) to the deep ultraviolet (AlN, Eg ∼ 6.2 eV). However, despite extensive research on these systems, several issues such as polarity control, role of strain, relaxation mechanisms, and In-content on dislocations and interface defects are still debated. As electron-hole recombination mechanisms at defects and interfaces strongly affect the efficiency of devices based on these alloys, the study and understanding of these issues is mandatory. The present contribution aims to investigate the role of doping, misfit and threading dislocations, and V pits in InxGa1-xN/GaN and AlxInyGa1-x-yN/GaN alloys with varying In concentrations. The work is focused on the results of electrical and optical characterization by surface photovoltage (SPV) spectroscopy. These results are compared with transmission electron microscopy analysis (TEM), light-assisted Kelvin probe force microscopy (KPFM), and deep level transient spectroscopy (DLTS) analyses in order to obtain a comprehensive picture of the carrier recombination at interface and defect states. The SPV signal is due to the illumination-induced change in the equilibrium surface potential, which is related to charge transfer and/or redistribution within the device. Surface photovoltage spectroscopy analyses surface potential as a function of the energy of incident photons. In SPV spectroscopy, electronic transitions are detected as changes in the slope of the spectra, which correspond to band-to-band transitions or intra-band transitions at the surface or interface of a multi-layered structure [4,5]. Figure 1 shows an example of such spectra on InxGa1-xN/GaN heterostructures, with different In content and Si doping level. The main features in the spectra allow for the extraction of the band gap energy both in the InxGa1-xN top layer and in the GaN substrate. Other features, like the minima indicated by the black arrow, allow us to investigate interface recombination phenomena. The comparison with other characterization results has allowed us to clarify the role of In content and misfit dislocations on electron-hole recombination mechanisms and to characterize the defects acting as strong recombination centres in ternary and quaternary GaN-based alloys. References [1] S. Zhou et al, (2018) Scientific Reports 8, 11053 [2] H. Li et al, (2018) Appl. Phys. Lett. 112, 073501 [3] J.K. Sheu et al, (2017) Sol. Energy Mater. Sol. Cells 166, 86-90 [4] L. Kronik, Y. Shapira, (1999) Surf. Sci. Rep. 37, 1-206 [5] D. Cavalcoli, M.A. Fazio, (2019) Mat. Sci. in Sem. Processing 92, 28-38
Defective State Studies in III-Nitride Alloys by Surface Photovoltage Spectroscopy
D CavalcoliSupervision
;M. A. FazioMembro del Collaboration Group
;A MinjMembro del Collaboration Group
2019
Abstract
High quality ternary (InGaN) and quaternary (AlInGaN) alloys have attracted a great attention in the last 20 years due to the large progress in epitaxial growth techniques which has led to the demonstration of highly efficient optical devices and solar cells [1], high electron mobility transistors [2], and, recently, photo-electrochemical (PEC) devices for water splitting cells [3]. These alloys show a bandgap tunable with composition, covering the whole spectrum from the infrared (InN, Eg ∼ 0.7 eV) to the deep ultraviolet (AlN, Eg ∼ 6.2 eV). However, despite extensive research on these systems, several issues such as polarity control, role of strain, relaxation mechanisms, and In-content on dislocations and interface defects are still debated. As electron-hole recombination mechanisms at defects and interfaces strongly affect the efficiency of devices based on these alloys, the study and understanding of these issues is mandatory. The present contribution aims to investigate the role of doping, misfit and threading dislocations, and V pits in InxGa1-xN/GaN and AlxInyGa1-x-yN/GaN alloys with varying In concentrations. The work is focused on the results of electrical and optical characterization by surface photovoltage (SPV) spectroscopy. These results are compared with transmission electron microscopy analysis (TEM), light-assisted Kelvin probe force microscopy (KPFM), and deep level transient spectroscopy (DLTS) analyses in order to obtain a comprehensive picture of the carrier recombination at interface and defect states. The SPV signal is due to the illumination-induced change in the equilibrium surface potential, which is related to charge transfer and/or redistribution within the device. Surface photovoltage spectroscopy analyses surface potential as a function of the energy of incident photons. In SPV spectroscopy, electronic transitions are detected as changes in the slope of the spectra, which correspond to band-to-band transitions or intra-band transitions at the surface or interface of a multi-layered structure [4,5]. Figure 1 shows an example of such spectra on InxGa1-xN/GaN heterostructures, with different In content and Si doping level. The main features in the spectra allow for the extraction of the band gap energy both in the InxGa1-xN top layer and in the GaN substrate. Other features, like the minima indicated by the black arrow, allow us to investigate interface recombination phenomena. The comparison with other characterization results has allowed us to clarify the role of In content and misfit dislocations on electron-hole recombination mechanisms and to characterize the defects acting as strong recombination centres in ternary and quaternary GaN-based alloys. References [1] S. Zhou et al, (2018) Scientific Reports 8, 11053 [2] H. Li et al, (2018) Appl. Phys. Lett. 112, 073501 [3] J.K. Sheu et al, (2017) Sol. Energy Mater. Sol. Cells 166, 86-90 [4] L. Kronik, Y. Shapira, (1999) Surf. Sci. Rep. 37, 1-206 [5] D. Cavalcoli, M.A. Fazio, (2019) Mat. Sci. in Sem. Processing 92, 28-38I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
