Doping Control of AlInN/GaN Lattice-Matched Heterostructur


Yoshitaka Taniyasu, Jean-François Carlin*, Antonino Castiglia*,
Raphaël Butté*, and Nicolas Grandjean*
Materials Science Laboratory,
*Ecole Polytechnique Fédérale de Lausanne

   Among III-nitride semiconductors, AlInN is the only ternary alloy that can be grown lattice-matched to GaN at an In composition of 17 % [1]. Lattice-matched AlInN/GaN heterostructures should be free from cracks, strain-driven composition inhomogeneities, and strain-related defects, which are limiting the performance of ultraviolet/visible light-emitting diodes (LEDs) and laser diodes (LDs) when using conventional lattice-mismatched AlGaN/GaN or InGaN/GaN heterostructures. In addition, an AlInN/GaN structure has a large bandgap discontinuity and a large refractive index contrast even at the lattice-matched condition [1], which leads to strong carrier and optical confinements. Thus, AlInN/GaN structures are expected not only to improve the device properties but also to increase the design flexibility for novel III-nitride devices.
   Doping control of AlInN lattice-matched to GaN is crucial for device applications. However, non-intentionally doped AlInN has so far shown n-type conduction with high residual donor concentration, which is a significant obstacle to p-type doping as well as to intentional n-type doping. To reduce the residual donor concentration, we grew AlInN under an In-rich condition to benefit from the In surfactant effect. Then, n-type conduction of AlInN was intentionally controlled by Si doping. On the other hand, we found that one of the compensating defects for p-type doping is related to the presence of surface pits. By decreasing the pit density, p-type AlInN was successfully obtained by Mg doping (Fig. 1) [2].
   Using p-type AlInN, we fabricated InGaN/GaN multiple quantum wells (MQWs) LEDs. The LEDs show light emission at a wavelength of 445 nm, which corresponds to electron-hole recombinations occurring in the InGaN/GaN MQWs (Fig. 2). This confirms the efficient hole injection from the p-type AlInN layer to the MQWs. The achievement of p-type as well as intentional n-type AlInN will open further new possibilities for III-nitride devices.

[1] J.-F. Carlin and M. Ilegems, Appl. Phys. Lett. 83 (2003) 668.
[2] Y. Taniyasu, J.-F. Carlin, A. Castiglia, R. Butté, and N. Grandjean, Appl. Phys. Lett. 101 (2012) 082113.

Fig. 1. Net acceptor concentration NA - ND of Mg-doped AlInN with high and low pit density as a function of Mg flow rate. Inset: AFM image of AlInN surface.
Fig. 2. Electroluminescence of InGaN/GaN MQW LEDs using p-type Mg-doped AlInN with high and low pit density.