Short period p-type AlN/AlGaN superlattices for deep UV light emitters.
- PDF / 159,586 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 39 Downloads / 205 Views
1202-I10-03
Short period p-type AlN/AlGaN superlattices for deep UV light emitters. S. Nikishin1, B. Borisov1, V. Mansurov1, M. Pandikunta1, I. Chary1, G. Rajanna1, A. Bernussi1, Yu. Kudryavtsev2, R. Asomoza2, K. A. Bulashevich3, S. Yu. Karpov3, S. Sohal1, and M. Holtz1 1 Nano Tech Center, Texas Tech University, Lubbock, TX 79401, USA 2 SIMS Laboratory of SEES, CINVESTAV, Mexico D.F.07300, Mexico 3 STR Group – Soft-Impact, Ltd., St. Petersburg, 194156, Russia ABSTRACT The Mg doped AlN/AlxGa1-xN (0.03 ≤ x ≤ 0.05) short period superlattices (SPSLs) were grown by gas source molecular beam epitaxy on (0001) sapphire substrates. The average AlN mole fraction is ~ 0.7 and the hole concentration is ~ 7×1017 cm-3. Contacts formed to the SPSLs using Ni/Au bilayer are found to have specific contact resistance ~ 5×10-5 Ωcm2 near room temperature and to show weak temperature dependence attributed to activation of Mg acceptors in the AlN barriers of SPSLs. These p-SPSLs are attractive for fabrication of transparent low resistive ohmic contacts for deep UV LEDs. INTRODUCTION AlxGa1-xN alloys with energy gaps from 3.4 in GaN to 6.2 eV in AlN can be grown epitaxially in the wurtzite structure across the full composition range using several methods, including gas source molecular beam epitaxy (GSMBE) with ammonia. This provides a wide range of possible emission wavelengths for photonic devices. However, device preparation is
Fig. 1. Mg incorporation in AlGaN grown at ~ 830 oC. III-N ratio and Mg flux are constant. fundamentally limited by the difficulties of preparing p-type layers of wide-bandgap AlxGa1-xN. Figure 1 summarizes our prior investigations on efficiency of Mg incorporation in AlxGa1-xN (0≤x≤1) when all layers are grown at the same temperature, III/N ratio, and Mg flux [1]. The resulting hole concentration obtained using Hall measurements is also shown for two samples. Reduction in the hole concentration, when x increases, is due to increasing Mg activation energy and reducing Mg incorporation in Al-rich alloys. These factors have driven us to develop AlN/AlGaN short period superlattices (SPSLs) allowing high hole concentrations in wide bandgap alloys with average AlN concentration up to 70% [2 – 4]. These structures, consisting of 3-6 monolayer (ML) thick barriers of AlN and 2-3 ML thick wells of AlxGa1-xN, have been shown to have optical bandgaps in the deep UV suitable for light emitting diodes (LEDs)
operating down to ~ 250 nm [5]. However, until now there has been no systematic investigation of the influence of Mg incorporation on growth rate and polarity of the well and barrier materials. Furthermore, the mechanism of current injection in (Ni-Au)/(p-AlGaN) ohmic contacts has been discussed [6, 7], although the temperature behavior of such contacts for pSPSL is unknown. In this paper, we report on the structural, compositional, and electrical properties of ptype Mg-doped SPSLs with a range of Mg concentrations, NMg, from 1018 to 1020 cm-3. We have found the Mg excess at the initial stage of p-SPSL growth to be c
Data Loading...
