Self-Organization of InAs/InP Quantum Dot Multilayers

Navdeep Singh Dhillon

Overview

Regimes of 3-D self-organization in quantum dot layers described using– Experimental observations for InAs/InP(001)

system– Atomistic Strain calculations

Pseudophase diagram developed to explain transition from vertically aligned to anti-aligned layers

Motivation

Periodicity and size uniformity of quantum dots grown in Stranski-Krastanov mode important for device applications

Detailed understanding of physical origin of phenomena prerequisite for obtaining the required 3-D arrangement for particular application

Stranski-Krastanov growth

InP(001) substrate

Low-Pressure Metal-Organic Vapor Phase Epitaxy in a cold-wall reactor

Stranski-Krastanov growth

InP substrate

InAs

3-7 ML of InAs is deposited

Stranski-Krastanov growth

InP substrate

InAs Islands

60 s treatment in TBAs/H2 ambient

The InAs monolayers form islands due to Interlayer Strain

Stranski-Krastanov growth

InP substrate

InAs Islands

Deposit Spacer layer and repeat

2 Regimes of Self-organization

Vertically Aligned (VA) Anti-Aligned (AA)

Quantum Dot Array Modeling

H Spacer Thicknessh QD heigthb QD baseD Lateral Spacing

C Vertically aligned point

A1, A2, A3Anti-aligned points

Experimental Results

Alignment depends mainly on H/D

Slight dependence on b/D

No direct dependence on h

Atomistic Strain Calculations

Keating’s valence force field method

Atomic coordinates relaxed using a conjugate-gradient algorithm until a minimum of elastic energy is found

16.6 < D < 29 nm 3.3 < b < 15.8 nm 1.2 < h < 3.6 nm

Conclusions

Self-organization of quantum dot multilayers– Spacer layer thickness (H)– Areal density of islands (D)– Lateral dimension (b) (to a lesser extent)

D b

H