Thesis presented December 16, 2015
Abstract: This thesis reports on the realization of photonic devices based on nitride wires. Self-assembled GaN wires were grown without catalyst by metal-organic vapor phase epitaxy (MOCVD) on sapphire substrates. Part of this work focused on the selective area growth of GaN wires through a dielectric SiN
x mask with regular arrays of holes defined by lithography and dry etching. We studied the influence of the growth conditions (temperature, pressure, V/III ratio) and pattern geometry on the homogeneity of the selective area growth. These wires were used as templates for the growth of core-shell InGaN/GaN heterostructures. In addition, the growth, microfabrication process and properties of three types of devices were studied:
- Single wire solar cells. We compared the efficiency of two type of heterostructures: shells composed of thick In
0.1Ga
0.9N layers and In
0.18Ga
0.82N/GaN quantum wells. After optimization of the electrical contact on the p-GaN shell, a maximal conversion efficiency of 0,33 % was obtained on single GaN wires with a shell of 30 quantum wells under 1 sun illumination (AM1.5G). Photocurrent spectroscopy revealed that the wire absorption edge varied between 400 and 440 nm.
- An integrated photonic platform. The system, that operates around
λ 400 nm, is composed of two GaN wires with radial InGaN/GaN heterostructures positioned on the same substrate and coupled with a SiN
x waveguide. The electrical characterization of the platform revealed a switching speed inferior to 0.25 s without persistent photocurrent.
- Flexible light emitting diodes (LED). The LED fabrication is based on a dual approach which associates inorganic InGaN/GaN emitters (λ=400-470 nm) and a polymer. The wires are encapsulated in a PDMS matrix before being detached from their native substrate. Electrical contacts are made with silver nanowires which are flexible, highly conductive and transparent in the visible range. Based on this procedure a two-color LED was realized by stacking a blue and a “green” LED.
Keywords: Nanowire, Nitride, Photonics, Photovoltaics, Light emitting diode, Selective area growth
On-line thesis.