D. Vaufrey

Inductively coupled plasma (ICP) etching of N-polar n-doped gallium nitride (GaN) with a CH4/H2/Ar chemistry was investigated as a function of CH4 ratio in the gas mixture, DC bias voltage, ICP source power, pressure, and total gas flow. Two etching modes are evidenced when varying CH4 ratio in the gas mixture, the DC bias voltage at fixed source power or the total gas flow. Moreover, the etch rate increases with increasing DC bias voltage at 1000 W source power, increasing source power or decreasing pressure. In some conditions, the formation of a polymer film onto the GaN surface was observed. Etch rates as high as 65 nm/min was achieved. Based on the competition between GaN etching and polymer layer deposition observed from the etch rate study, an etching mechanism of GaN with a CH4/H2/Ar chemistry is proposed. This study proposes an overview of etching performances of GaN with both Cl2/Ar and CH4/H2/Ar chemistries. The luminescence properties and GaN surface chemistry for a given set of plasma parameters in the CH4-based chemistry were investigated by cathodoluminescence, x-ray photoelectron spectroscopy, and hard x-ray photoelectron spectroscopy, respectively. The GaN properties after etching were compared to the ones obtained after a Cl2/Ar etching chemistry. Preliminary results suggest that the CH4-based etched samples exhibit improved electro-optical performance.

The full InGaN structure is used to achieve red light emitting diodes (LEDs). This LED structure is composed of a partly relaxed InGaN pseudo-substrate fabricated by Soitec, namely, InGaNOS, a n-doped buffer layer formed by a set of In_xGa_1−xN/GaN superlattices, thin In_yGa_1−yN/In_xGa_1−xN multiple quantum wells, and a p doped In_xGa_1−xN area. p-doped InGaN layers are first studied to determine the optimal Mg concentration. In the case of an In content of 2%, an acceptor concentration of 1 × 10¹⁹/cm³ was measured for a Mg concentration of 2 × 10¹⁹/cm³. Red electroluminescence was then demonstrated for two generations of LEDs, including chip sizes of 300 × 300 μm² and 50 × 50 μm². The differences between these two LED generations are detailed. For both devices, red emission with a peak wavelength at 620 nm was observed for a pumping current density of 12 A/cm². Red light-emission is maintained over the entire tested current range. From the first to the second LED generation, the maximum external quantum efficiency, obtained in the range of 17–40 A/cm², was increased by almost one order of magnitude (a factor of 9), thanks to the different optimizations.

Innovative PIN OLED that use a new n‐doped architecture have been investigated. Good initial performances as well as good lifetimes have been demonstrated. Thermal stability of these new diodes has been greatly improved by using a new system matrix+ n‐dopant. As a result, RGB diodes can sustain at least a 500 h storage period‐of‐time at 90 °C with minor degradation. Preliminary studies at 110 °C for at least 24 h show also very promising features for such devices.