High Power 330 nm AlInGaN UV LEDs in the High Injection Regime
- PDF / 658,518 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 49 Downloads / 184 Views
Y1.8.1
High Power 330 nm AlInGaN UV LEDs in the High Injection Regime M. Gherasimova1, J. Su1, G. Cui1, J. Han1, H. Peng2, E. Makarona2, Y. He2, Y.-K.Song2, A. V. Nurmikko2 1 Department of Electrical Engineering, Yale University, P.O. Box 208284, New Haven, CT 06520 2 Division of Engineering, Brown University, 182 Hope Street, Providence, RI 02912 ABSTRACT We report on the growth and testing of the light emitting diode structures incorporating quaternary AlInGaN active region with an emission wavelength of 330 nm. Small area circular devices were fabricated, yielding the output power of 110 µW measured with a bare-chip configuration in a high current injection regime (8 kA/cm2 for a 20 µm diameter device). Structural properties of the constituent epitaxial layers were evaluated by atomic force microscopy and transmission electron microscopy, resulting in the observation of two-dimensional growth morphologies of AlN and AlGaN, and the estimate of threading dislocation densities in the low 109 cm-2 range in the structures grown on sapphire substrates. INTRODUCTION III-nitride based ultraviolet (UV) light emitting diodes (LEDs) with emission wavelengths below 360 nm will inevitably incorporate Al as one of the alloy constituents and require epitaxial material optimization in order to improve device performance. Numerous potential applications, including biological agent detection, high-density optical storage, and non-line-of-sight communications, will benefit from the realization of the high-power compact UV emitters. It has been observed that the incorporation of high levels of Al in AlGa(In)N leads to the decrease in radiative efficiency and electrical conductivity in the material, yet the exact nature of the decline is not completely understood. To date, AlGaN and AlInGaN-based UV LEDs with emission wavelengths ranging between 260 and 360 nm have been reported by several groups [1-7]. In this paper we report on the fabrication and characteristics of the UV LEDs with peak emission wavelength of 330 nm, and discuss the properties of the AlGa(In)N material that are likely to affect the device performance. EXPERIMENTAL DETAILS The material growth was carried out by metalorganic chemical vapor deposition (MOCVD) in a horizontal-flow reactor (Aixtron 200/4 HT-S) using trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn) and ammonia (NH3) as sources of group III and group V elements, and bis(methylcyclopentadienyl) magnesium (Cp2Mg) and silane (SiH4) as dopants. A typical LED structure incorporates a 0.3 µm thick AlN buffer prepared by a two-step process whereby AlN is grown at 1150 ºC on a 20 nm nucleation layer deposited directly on sapphire at 500 ºC. High temperature (HT) AlN is grown at the reactor pressure of 60 mbar, with NH3 and TMAl flows of 6 standard
Y1.8.2
cubic centimeters per minute (sccm) and 20 µmol/min, respectively. The N-type region of the device is typically comprised of a 2.2 µm thick N-type Al0.26Ga0.74N doped with 1019 cm-3 of silicon, as determined by secondary ion mass spe
Data Loading...
