In-situ NC-AFM measurements of high quality AlN(0001) layers grown at low growth rate on 4H-SiC(0001) and Si(111) substrates using ammonia molecular beam epitaxy

Florian Chaumeton,Sébastien Gauthier,David Martrou

doi:10.1063/1.4922193

Abstract

Nitride wide-band-gap semiconductors are used to make high power electronic devices or efficient light sources. The performance of GaN-based devices is directly linked to the initial AlN buffer layer. During the last twenty years of research on nitride growth, only few information on the AlN surface quality have been obtained, mainly by ex-situ characterization techniques. Thanks to a Non Contact Atomic Force Microscope (NC-AFM) connected under ultra high vacuum (UHV) to a dedicated molecular beam epitaxy (MBE) chamber, the surface of AlN(0001) thin films grown on Si(111) and 4H-SiC(0001) substrates has been characterized. These experiments give access to a quantitative determination of the density of screw and edge dislocations at the surface. The layers were also characterized by ex-situ SEM to observe the largest defects such as relaxation dislocations and hillocks. The influence of the growth parameters (substrate temperature, growth speed, III/V ratio) and of the initial substrate preparation on the dislocation density was also investigated. On Si(111), the large in-plane lattice mismatch with AlN(0001) (19%) induces a high dislocation density ranging from 6 to 12×1010/cm2 depending on the growth conditions. On 4H-SiC(0001) (1% mismatch with AlN(0001)), the dislocation density decreases to less than 1010/cm2, but hillocks appear, depending on the initial SiC(0001) reconstruction. The use of a very low growth rate of 10 nm/h at the beginning of the growth process allows to decrease the dislocation density below 2 × 109/cm2.

Highlights

During the last four decades, the global demand for electrical energy has been multiplied by 3.3 and is growing faster than for all other forms of energy
SUMMARY The use of Non Contact Atomic Force Microscope (NC-AFM) coupled under ultra high vacuum (UHV) to a molecular beam epitaxy (MBE) chamber dedicated to the growth of aluminum nitride (AlN)
Layers by ammonia molecular beam epitaxy has offered a unique way to characterize the surfaces of the Si(111) or the 4H-SiC(0001) substrates and the surfaces of the AlN layers grown on them in different conditions

Summary

Introduction

During the last four decades, the global demand for electrical energy has been multiplied by 3.3 and is growing faster than for all other forms of energy. A solution to meet this demand is to integrate devices with greater operating high-powers, frequencies and temperatures. Wide band gap group-III nitride semiconductors are widely used for the elaboration of electronic devices with such capacities. The physical properties of nitride films are highly influenced by their defect density. In order to obtain high performance devices, it is imperative to reduce this defect density as much as possible. The elaboration of nitride semiconductor devices is very often started with an aluminum nitride (AlN) buffer layer, which can be grown on silicon (Si(111)),[1,2] silicon carbide (nH-SiC(0001))[3,4] or sapphire (Al2O3(0001)).[5]

Objectives

Conclusion