Molecular Beam Epitaxy

3Migration‐Enhanced Epitaxy and its Application

Yoshiji Horikoshi

Department of Science and Engineering, Waseda University, Tokyo, 169‐8050, Japan

3.1 Introduction

Thin‐film growth of III–V compound semiconductors usually occurs in a “layer‐by‐layer” manner, called the Frank Van der Merwe mode [1]. This process comprises the formation of small one‐monolayer (1‐ML) thick islands on an atomically flat surface and succeeding lateral growth from these islands because the periphery of the islands provides a high density of atomic steps. As a result, 1‐ML growth is completed. This ideal layer‐by‐layer growth, however, never occurs in the practical epitaxial growth of III–V compound semiconductors by molecular beam epitaxy (MBE) [2] and metalorganic vapor‐phase epitaxy (MOVPE) [3]. Because of the limited migration distance of deposited atoms on the surface, new islands tend to be formed before completing the first monolayer. Thus, the resulting surface suffers from roughness up to several monolayers high for the growth of 1000‐nm thick layers. Artificial enhancement of surface adatom migration is inevitable to solve this problem.

The most effective way to enhance the surface adatom migration is to deposit group III elements solely on the surface [4–6]. When the group III atoms are deposited without group V elements, so‐called Stranski–Krastanov mode [1] growth takes place, and a complete monolayer is formed when the amount of deposited group III atoms is 1 ML as a result of active migration. ...