Optical signatures of silicon and oxygen related DX centers in AlN

Abstract

Bulk AlN crystals typically contain high concentrations of oxygen, silicon, and carbon À as also state-of-the art epitaxial layers typically do, depending on the specific growth conditions. In optical spectroscopy, such crystals show broad bands in the region from 2-5 eV in absorption and emission. We investigated several emission bands in the range from 1.4 to 1.9 eV, especially those centred at 2.0 and 2.4 eV, which under below-bandgap excitation with a 325 nm laser dominate the photoluminescence (PL) spectra both at low and at room temperature. We find clear indications that all these transitions occur between different states of the shallow donors Si or O, and deep acceptors. The donors undergo lattice relaxation and form DX centres. Depending on temperature, the initial state is either a long-lived (S ¼ 1) DXcentre state of the donors, a shallow EMT-like conventional donor state, or a free electron À with markedly different relaxation times for the optical transitions under below-bandgap excitation. The acceptor involved in these PL bands is likely linked to aluminum vacancies. Based on our data, we develop configuration coordinate diagrams and a combined level scheme for multiple transitions in the range from 1.4 to 2.4 eV.Tentative level scheme for PL bands observed in AlN in the range from 1.4 to 2.4 eV.

Shallow donor and DX state in Si doped AlN nanowires grown by molecular beam epitaxy

“…At higher temperature, an ionization energy of 270 meV is found, which is attributed to the DX state of Si 33,34,[46][47][48] . Interestingly, S0 and S800 exhibit a higher activation energy of around 700 meV at high temperature, which is inferred from the ionization energy of residual oxygen in DX state in AlGaN 49 .…”

Single-Photon Emission from Point Defects in Aluminum Nitride Films

“…For these SPEs, point defects in wide-bandgap semiconductors are one of the more promising quantum emitters that have been studied recently, due to their unique properties and potential applications. − To date, defect-related SPEs have been reported in wide-bandgap semiconductors, such as in diamond, zinc oxide, silicon carbide (SiC), hexagonal boron nitride (hBN), and gallium nitride. − Aluminum nitride (AlN) is also a wide-bandgap semiconductor with an optical transition energy of approximately 6.1 eV. AlN is a key semiconductor for next-generation photonic and electronic devices, especially in high-power electronics and high-temperature applications. , Recently, defect-related absorption and photoluminescence (PL) have been reported in AlN. − For example, Lamprecht et al discussed a model for the deep defect-related emission bands between 1.4 and 2.4 eV . Schulz et al investigated defect-related PL in the near UV region between 3 and 4 eV .…”

Photochromism and influence of point defect charge states on optical absorption in aluminum nitride (AlN)

“…The highest value is attributed to V N vacancies 58 since the heavy surrounding Al atoms vibrate at very low frequency. In case of DX-states, the energy difference between the thermal activation depth and the absorption peak can be significantly higher; 37,38,[64][65][66] probably up to 1.8 eV. In the following sub-sections, we detail and summarize the data for each of the absorption bands in the B2 area of the AlN sample.…”

“…These three impurities provide not only isolated substitutional defects (i.e., oxygen and carbon substituting nitrogen, and silicon substituting aluminum: O N, C N, Si Al ), [17][18][19][20][21][22] but are also assumed to form complexes, such as V Al -nSi Al , 23 V Al -nO N (n=1…4 is a number of Si or O atoms), 13,14,16,[23][24][25][26][27][28] C N -Si Al , 29 carbon pairs, 30 and tri-carbon complexes. 31 Usually, defects can have several allowed charge states in the bandgap, 32,33 including DXstates, [34][35][36][37][38] resulting in the polymorphism of defects properties. The current charge states of defects are given by the Fermi level which should be known first for a successful characterization of AlN crystals.…”