Improved InGaN Epitaxial Quality by Optimizing Growth Chemistry

Investigating Organization
Sandia National Laboratories

Principal Investigator(s)
Dr. J. Randall Creighton

Subcontractor
None

Funding Source
Building Technologies Program/NETL

Award
DOE Share: $785,000

Contract Period
8/01/07 – 7/31/09

The goal of the Sandia National Laboratory is to develop high-efficiency green (530 nm) light emitters based on improvement in InGaN epitaxial material quality.  High indium compositions needed for green emission are very difficult to obtain.  Limited thermodynamic stability and unwanted parasitic chemical reactions are two fundamental roadblocks to controllable and efficient epitaxial growth.  This proposal addresses improvement of InGaN active regions. Improved growth efficiency and control of indium incorporation will also enable better LED manufacturability.

Parasitic gas-phase reactions during film growth have been shown to form unwanted gas-phase nanoparticles during GaN, AlN, and AlGaN growth.  For Al containing films, these nanoparticles are responsible for a loss of up to 80% of the input Al, resulting in growth inefficiency and poorly controlled alloy composition.  Preliminary experiments showed that nanoparticles are also formed during InGaN growth.  It is thus important to characterize and understand the complex parasitic gas-phase chemistry in InGaN growth. In situ laser light scattering will be used to examine InGaN nanoparticle formation in detail, with particular emphasis on the role of the carrier gas composition, V/III ratio, residence time, and temperature.  A thermophoretic sampling technique and ex situ transmission electron microscopy will be used to examine InGaN nanoparticle structure and composition.  A variety of experimental methods, including in situ FTIR, will be employed to determine the exact role that hydrogen (versus nitrogen) carrier gas plays in the InGaN growth process.

Thermodynamic and surface kinetic effects also limit In-incorporation.  The InGaN film growth chemistry and alloy stability will be studied as a function of growth conditions.  A large database of InGaN growth rates and composition over a wide range of MOCVD conditions will be generated, followed by the measurement of the InGaN film desorption (or evaporation) rates using in situ reflectometry.  These measurements will quantitatively determine the thermodynamic or kinetic stability of InGaN films as a function of temperature and gas-phase composition.  Using the knowledge gained, a quantitative and predictive reactor-scale model of the combined (parasitic) gas-phase chemistry and thin-film growth process will be developed and used to optimize In-incorporation.  The ultimate goal will be improved InGaN quantum well internal quantum efficiency (IQE) through higher-temperature growth of high In-content films.  Using optimized growth conditions (e.g. higher temperature) a 2X improvement in IQE for standard 530 nm InGaN multiquantum well (MQW) structure will be demonstrated.

Content dated 2/08