Indium Surface Segregation during Growth of (In,Ga)N/GaN Multiple Quantum Wells by Plasma-Assisted Molecular Beam Epitaxy

Abstract

We investigate the synthesis of (In,Ga)N/GaN multiple quantum wells by plasma-assisted molecular beam epitaxy. For metal-stable growth, reflection high-energy electron diffraction and X-ray diffraction reveal massive In surface segregation which is directly confirmed by In depth profiles recorded by secondary-ion mass-spectrometry. These profiles exhibit a top-hat In distribution and are thus indicative of a zero order segregation mechanism instead of a first order process as observed for other materials systems. The segregation of In during metal-stable growth results in quantum wells with smooth interfaces but larger width than intended, and thus causes blue-shifted transition energies and poor quantum efficiency. This unexpected blue-shift may be the reason for the frequent conclusion that the theoretical polarization fields of Bernardini et al. [Phys. Rev. B 56, R10024 (1997)] are too large for (In,Ga)N. Being in possession of the (at least approximately) correct structural parameters, we find the theoretical fields of Bernardini et al. for (In,Ga)N to be in very satisfactory agreement with the experimental data. Reduction of In segregation by N-stable conditions is possible but inevitably results in rough interfaces.

Progress in Indium Gallium Nitride Materials for Solar Photovoltaic Energy Conversion

“…[25] A large nitrogen flux is believed to provide additional nitrogen bonding sites for indium atoms that might otherwise evaporate away or segregate out of the bulk In x Ga 1Àx N and form a separate indium phase. [110] Despite this, the difficulty in growing high-quality In-rich films remains the biggest challenge to the development of efficient In x Ga 1Àx N solar cells. New growth techniques and conditions are required to develop more compositionally homogeneous, highly crystalline In x Ga 1Àx N films with improved photovoltaic properties.…”

Correlated high-resolution x-ray diffraction, photoluminescence, and atom probe tomography analysis of continuous and discontinuous InxGa1−xN quantum wells

“…19 The more diffuse upper interface is believed to result from indium segregation during QW growth. [26][27][28] Indium atoms accumulate on the surface during growth of the In x Ga 1Àx N layer, enabling the excess indium to diffuse into the GaN barrier layer and producing an asymmetric profile. The measured QW composition profiles were …”

Crecimiento, fabricación y caracterización de diodos electroluminiscentes basados en pozos cuánticos de InGaN

“…En todas las muestras se observó una reconstrucción (2x2) en el patrón de RHEED durante el enfriamiento del substrato desde la temperatura de crecimiento del GaN hasta la del InGaN (figura 6.12). Así mismo, después de cerrar el obturador de Indio tras el crecimiento del pozo cuántico, y transcurrido un tiempo de crecimiento de la barrera, se observa una reconstrucción (1x3) en el azimut [1-100], (figura 6.12) que ha sido asociada a un recubrimiento parcial de la superficie por el Indio que se segrega durante el crecimiento del ternario [Walt01].…”

“…El tomar como tiempo de crecimiento del pozo el tiempo nominal más el que transcurre hasta que aparece la reconstrucción (1x3) en la barrera lleva a estimaciones más apropiadas de los espesores de pozo y barrera, como se ha observado en la literatura [Walt01].…”