On the origin of red luminescence from iron-doped β-Ga2O3 bulk crystals

Abstract

Currently, Fe doping in the ~10 18 cm-3 range is the most widely-available method for producing semi-insulating single crystalline-Ga 2 O 3 substrates. Red luminescence features have been reported from multiple types of Ga 2 O 3 samples including Fe-doped-Ga 2 O 3 , and attributed to Fe or N O. Herein, however, we demonstrate that the high-intensity red luminescence from Fe-doped β-Ga 2 O 3 commercial substrates consisting of two sharp peaks at 689 nm and 697 nm superimposed on a broader peak centered at 710 nm originates from Cr impurities present at a concentration near 2 ppm. The red emission exhibits twofold symmetry, peaks in intensity for excitation near absorption edge, seems to compete with Ga 2 O 3 emission at higher excitation energy and appears to be intensified in the presence of Fe. Based on polarized absorption, luminescence observations and Tanabe-Sugano diagram analysis, we propose a resonant energy transfer of photogenerated carriers in-Ga 2 O 3 matrix to octahedrally-coordinated Cr 3+ to give red luminescence, possibly also sensitized by Fe 3+ .

Magneto-optical properties of Cr3+ in β-Ga2O3

“…It was suggested that the internal transitions between the 2 E and 4 A 2 states of Cr 3þ give rise to two sharp emission (or absorption) lines at around 1.78 and 1.80 eV at room temperature (RT), which were labeled as R1 and R2 lines. 18,19,[22][23][24][25][26][27][28][29][30] This conclusion was based 19,22,23,25 on a similarity of the transition energies with the internal transitions of Cr 3þ in Al 2 O 3 . [31][32][33] They were further supported by the analysis of higher-lying excited states detected in absorption 19,28 and emission 18,22,[24][25][26][27][28] spectra of Cr-doped b-Ga 2 O 3 , as well as photoluminescence excitation spectra of the R lines 24,26,28 using the Tanabe-Sugano diagrams.…”

Effect of extended defects on photoluminescence of gallium oxide and aluminum gallium oxide epitaxial films

“…Polarization dependence of emission is seen below the bandgap for all three samples. The observed red emission starting around 700 nm (1.77 eV) is due to the Fe-doped β-Ga 2 O 3 substrate on which the Si-doped β-Ga 2 O 3 films were grown 27 , 28 .

Figure 1 Polarized photoluminescence of β-Ga 2 O 3 grown on (010) Fe-doped β-Ga 2 O 3 excited at 267 nm (4.64 eV).

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Origin of Red Emission in β‐Ga2O3 Analyzed by Cathodoluminescence and Photoluminescence Spectroscopy

“…The origin of the red emission is quite ambiguous, and the literature provides three plausible explanations involving doping by transition metals or rare earth metals [ 10–14,19–21 ] or by nitrogen. [ 22,23 ] Figure 1b shows the CL spectra recorded in the region of 700 nm to provide more details in the near‐IR region of the spectrum.…”

“…This raises an important question on the origin of these transitions, which may well be due to other transition‐metal impurities such as Cr. [ 10,24 ] It is well known that even very low concentrations, of the order of ppm, of Cr can result in strong luminescence. [ 28,29 ]…”

“…The optical properties of β ‐ Ga 2 O 3 grown by various methods with different dopants have been widely reported, [ 5–9 ] primarily for emission in the UV and blue regions of the visible spectrum. However, there are only a few reports [ 10–14 ] on emission in the red spectral region due to transition metals, which is the focus of this work. We discuss red emission in relation to various dopants in β‐Ga 2 O 3 .…”