| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
O4, Fabrication and Characterization of 265 nm Light Emitting Diodes on AlN Single Crystal Substrates |
| Author(s) |
Ramón Collazo, Seiji Mita, Jinqiao Xie, Anthony Rice, James Tweedie, Rafael Dalmau, Baxter Moody, Raoul Schlesser, Ronny Kirste, Axel Hoffmann, Zlatko Sitar |
| On-Site Speaker (Planned) |
Ramón Collazo |
| Abstract Scope |
AlGaN alloys on AlN single crystal substrates have attracted considerable attention as the building blocks of current deep UV light emitting diode technology. In previous studies, AlGaN films with varying compositions and doping levels were deposited on homoepitaxial AlN layers grown on AlN single crystal substrates. If relaxation is not essential for a given application, relaxation schemes can be avoided altogether in favor of pseudomorphic AlGaN films on AlN. For compositions above 65% Al, the films were pseudomorphic. A light emitting diode grown on AlN single crystal substrates based on pseudomorphic AlGaN films will be described. In addition, an estimation of the internal quantum efficiency based on photoluminescence measurements for multi-quantum wells emitting at wavelengths between 245 nm and 270 nm was obtained. The structure was grown on a vicinal cut (0001)-oriented AlN single crystal substrate with an absorption coefficient of less than 50 cm<SUP>-1</SUP>. MOCVD was used for its deposition, using the typical precursors. The n-type layer was doped with Si to 1x10<SUP>19</SUP> cm<SUP>-3</SUP>, while the p-type layers were doped with Mg to 4x10<SUP>19</SUP> cm<SUP>-3</SUP>. The corresponding Si doping in this Al<SUB>0.75</SUB>Ga<SUB>0.25</SUB>N film yielded a sheet resistance of 100 Ω/☐. The structure was finished with a 200 nm p-GaN layer as hole injection layer. The active layer consists of a periodic structure of 5 nm AlN/ 1.5 nm Al<SUB>0.60</SUB>Ga<SUB>0.40</SUB>N repeated 4 times. The optical properties of this active layer were characterized by temperature dependent photoluminescence measurements from which an internal quantum efficiency (IQE) was estimated. These measurements were performed on different structures, emitting at three different wavelengths: 244 nm, 252 nm, and 261 nm. LED fabrication consisted of reactive ion etching to define the mesa structure and subsequent Ohmic contact metallization for the n- and p-type layers. The external quantum efficiency (EQE) is the product of the IQE and the light extraction efficiency. For emission around 260 nm, with an IQE of 43%, a light extraction efficiency of 12% is needed to achieve and EQE of 5%. For the fabricated LED described above, a rectification ratio of 10000 at 16 V is observed, along with a maximum current of 207 mA at 19 V. The turn-on voltage for this diode is below 10 V. Such a high turn-on voltage is expected if a GaN layer is used as the p-type layer for the junction, arising from the heterojunction discontinuity. The relatively larger turn-on voltage limits the possible wall-plug efficiency to 40% of the EQE, thus if an EQE of 5% is expected, the maximum wall-plug efficiency will be around 2%. The electroluminescence spectra showed LED emission at 265 nm with a FWHM of 11 nm. Precise EQE measurements and reliability measurements will be presented for the described LEDs. |
| Proceedings Inclusion? |
Undecided |