An increasing demand for bright and efficient ultraviolet light emitting diodes (UV-LEDs) is generated by numerous applications such as biochemical sensors, purification and sterilization, and solid-state white lighting. AlxGa1-xN is a promising material to develop UV-LEDs due to the direct wide-bandgap material for emission wavelengths in the UV range and the capability of n- and p-type doping. To develop UV-LEDs on Si substrates is very interesting for low-cost UV-light sources since the Si substrate is available at low cost, in large-diameter size enabling the integration with well-known Si electronics. This work presents the first crack-free AlGaN-based UV-LEDs on Si(111) substrates by MOVPE growth. This AlGaN-based UV-LED on Si(111) substrate consists of Al0.1Ga0.9N:Si layers on LT-AlN/HT-AlN SL buffer layers and an active layer of GaN/Al0.1Ga0.9N MQWs followed by Mg-doped (GaN/Al0.1Ga0.9N) superlattices and GaN:Mg cap layers. It yields a ~350 nm UV electroluminescence at room temperature and a turn-on voltage in a range of 2.6 - 3.1 V by current-voltage (I-V) measurements. The novel LT-AlN/HT-AlN superlattice buffer layers efficiently improve the crystalline quality of AlxGa1-xN layers and compensate a thermal tensile strain in AlxGa1-xN layers after cooling as observed by in-situ curvature measurements. The dislocation density could be reduced from 8.4E+10 cm-2 in the AlN-based SLs to 1.8E+1010 cm-2 in the Al0.1Ga0.9N layers as determined by cross-sectional transmission electron microscopy (TEM) measurements. Crack-free AlxGa1-xN layers grown on these LT-AlN/HT-AlN superlattices with were achieved on Si substrates with good crystalline, optical, and electrical properties. The best crystalline quality of Al0.1Ga0.9N was obtained with w-FWHMs of the (0002) and (10-10) reflections of ~700 and ~840 arcsec, respectively. The good optical qualities of Al0.1Ga0.9N and Al0.65Ga0.35N were presented with a low yellow luminescence and narrow near-bandgap emissions at 330 and 240 nm, respectively as determined by cathodoluminescence (CL) measurements. The maximum electron concentration of 2.6E+18 cm-3 in n-type Al0.1Ga0.9N:Si layers and a hole concentration of 2.4E+1017 cm-3 of Mg-doped GaN/Al0.1Ga0.9N superlattices were achievable. These high-quality AlxGa1-xN materials with good optical and electrical properties were the main factors to accomplish AlGaN-based UV-LEDs on Si(111) substrates. It is demonstrated that it is also a promising approach to achieve deep UV-LEDs on Si substrates with a higher Al content layers.
AlN, AlGaN, UV LEDs, Epitaxy, MOVPE, Si doping, Mg doping