Micro-structured light emission from planar InGaN light-emitting diodes

Abstract

Investigation of the surface modification of the p-type layer in GaN light-emitting diodes (LEDs) by exposure to a trifluoromethane plasma is reported. It is found that the plasma treatment reduces the conductivity of the p-GaN by several orders of magnitude, and when applied at room-temperature through a patterned mask, localized current channels into the active region of a p-in device are created. This provides a novel approach to laterally modulate the light emission from an LED over essentially planar areas. This technique allows the projection of high-resolution images from non-pixelated devices, and an example application of maskless pattern transfer with sub-micron features into photoresist is demonstrated.

Planar micro- and nano-patterning of GaN light-emitting diodes: Guidelines and limitations

“…This is even true for techniques (such as localized plasma-treatment) that change the electrical properties of the p-GaN because the present understanding is that the p-GaN is only affected in a very thin layer (an order of magnitude thinner than the p-GaN thickness) directly at the top-surface. 9 A final boundary to Eq. (3) is given at the interface to the junction region.…”

“…9,16 To understand how this is possible, we consider a device with nano-point current injection. In this case, the LED mesa was 4 Â 4 lm 2 , the mesa height 2 lm, and the overall n-GaN thickness 3 lm.…”

“…9 Alloys are very difficult to consider in this type of model because of their complex nature which involves significant effects from random alignment of phases, partial oxidation, and porosity. For comparison with the ITO simulation, a thin metallic current spreading layer made from 30 nm Pd was modelled as well.…”

“…Besides lighting, LEDs offer a wide range of potential applications including photo-excitation and optical manipulation tools for bio-photonics, 1-3 high-bandwidth emitters for visible light communications, 4-6 highly efficient colour conversion based on radiative or non-radiative transfer, 7,8 maskless lithography methods, 9 and micro-displays. 8 For many of these applications, it is beneficial or even mandatory for the emitter to be patterned on a micron-or in some cases even on a submicron scale.…”

“…This covers a whole range of techniques, all of which have in common that the LED mesa is macroscopic in size and the pattern is created by localizing the current injection into the p-GaN layer of the LED. 6,9,14 Such techniques tend to allow simpler fabrication of very small features compared to approaches based on etching and in GaAs-based infrared LEDs, sub-micron pattern definition was demonstrated in this way. 15,16 Localized current aperturing in III-nitride LEDs can be achieved for example by patterning the p-metal contact or by local variation of the contact resistivity between the current spreading layer and the p-GaN.…”