The document summarizes research on the effects of annealing on N-type indium arsenide (InAs) thin films grown on silicon substrates. Hall effect measurements and transmission electron microscopy analysis were used to analyze electrical properties and defect density. The results showed that annealing at 550°C decreased electron mobility by 7% and increased sheet resistance by 59% in the InAs films. Transmission electron micrographs revealed a higher defect concentration in the annealed samples, suggesting annealing relieved stresses but introduced more defects due to the mismatch between the InAs and Si crystal structures. Therefore, annealing had a negative impact on the electrical properties of thin InAs films for semiconductor applications.

1. Name: Israel Vega
High School: Immokalee High School
Research Advisor: Dr. Kevin S. Jones, University of Florida, Gainesville
Research Site: Department of Materials Science, University of Florida, Gainesville
ABSTRACT
With ever shrinking transistors, integrated circuits continue to have more computing power
to perform faster computations. According to Moore’s Law, the number of transistor’s per
square inch in integrated circuits doubles every year. For this trend to continue,
semiconductor materials must be improved to fabricate smaller faster transistors . That is
why there is a high interest of using novel materials, specifically N-type InAs grown on Si. N-
type InAs has a higher concentration of free electrons, since dopants are introduced to
modify its electrical properties. InAs has a high electron mobility and narrow band gap that
allows fast transfer of electrons to operate signals. InAs and Si both have a diamond cubic
crystalline structure which is ideal ,because similar crystal lattices between semiconductors
will minimize defects such as vacancies and misalignments in the arrangement of atoms in
the crystal. Defects in crystal lattice degrade the performance of the semiconductor
conductivity. InAs has a larger diamond cubic structure than Si which limits its performance
to be used in transistors. N-type MOCVD thin films of InAs were annealed at a higher
temperature than they were grown in to observe changes in their structure. Samples of
annealed and non-annealed InAs were analyzed for their electrical properties by using Hall
Effect Measurements to determine conductivity, carrier concentration, electron mobility,
resistivity, and sheet resistance. Plan view TEM observations were conducted to analyze the
samples microstructure for differences in defect density.
INTRODUCTION
All of electronic devices are made up of transistors that amplify or block electrical signals
which operate in a binary system of on and off signals. With many networking transistors,
signals can be sent, stored and translated into complex combinations to perform operations
on your electronic device. Transistors are made of semiconductor material which uses both
its conductive and insulating properties to amplify or block electrical signals in devices. Over
the years, the number of transistors on electrical circuits grows and the size of the transistors
shrinks. Smaller and numerous transistors establishes more computing power to operate
more electrical signals. This exponential rate is known as Moore's law and for this
observation to hold true, semiconductor materials must be improved for smaller and faster
transistors, which is why there is a high interest of using N-type InAs on Si. N-type InAs has
high electron mobility and a narrow band gap to allow faster transfer of electrons. InAs and Si
both have a diamond cubic crystalline structure; however InAs has a larger diamond cubic
structure than Si which limits its performance to be used as a semiconductor. In this project,
grown thin films of InAs were analyzed for the effects of annealing on the InAs’s conductivity,
carrier concentration, and electron mobility.
RESULTSMETHOD
Samples of N-Type InAs grown on Si wafer were prepared in 1cm² squares for Hall Effect
Measurement and Plane View TEM observation. A non-annealed sample served as a control
that had MOCVD InAs grown on Si between 300°C and 350°C and was analyzed for its
electrical properties by conducting a Hall Effect Measurement by setting the sample on a four
probe Hall Effect sensor. Each corner was coated with the soft metal Indium to connect
contacts with the four probes. It’s important that the contacts on each of the corners are
ohmic to receive an accurate reading from Hall Effect measurement and can be determined
by using a curve tracer. These samples need to be coated by an atomic layer deposition of
Aluminum Oxide to keep the Arsenide from evaporating during the annealing process. The
sample is then annealed in a furnace at 550 °C for 10 minutes with Argon purging to keep the
sample from reacting with the atmosphere at this high temperature. The sample is then left
to cool at room temperature. After cooling, the annealed sample is bathed in a buffered
oxide etch with hydrofluoric acid for 10 minutes to remove the Aluminum Oxide coating. The
annealed sample is bathed in water to remove the acid and then dried. A Hall Effect
Measurement is conducted on the annealed sample to analyze conductivity, carrier
concentration, electron mobility, resistivity and sheet resistance. Both annealed and non-
annealed samples are prepared for Plane-view TEM analysis. Using a Focused Ion Beam, the
samples will have a small surface of its InAs etched off to analyze for defect density by TEM
analysis. It’s important to have very thin samples for Plan-view TEM analysis. If the sample is
too thick, the electrons won’t be able to pass right through the sample and not properly view
internal defects.
DISCUSSION
Hall Effect Measurements show that annealed samples have higher sheet resistance and
lower mobility than non-annealed samples. In fact, the average mobility of non-annealed
InAs was -29.633 (cm2/Vs), average sheet number was -2.6E13 (cm-2) and the average sheet
resistance was 8,283.5 (Ohm/cm2). The average mobility of the annealed sample was -
27.4383(cm2/Vs), average sheet number was -3.0945E13 (cm-2) and average sheet
resistance was 13,189.5 (Ohm/cm2). This a 7% decrease of mobility in the annealed sample,
19% increase in sheet number, and a 59% increase in sheet resistance. The Hall Effect
Analysis also shows miniscule change in the amount of carriers, which suggests annealing at
550°C does not deactivate or activate dopants. The decrease in mobility of the annealed
sample can be seen in the TEM images. Strains and defects are still distributed across the
annealed sample. Because the annealed sample has a lower mobility than the non-annealed,
there must be a higher defect concentration in the annealed sample than the non-annealed.
Effects of Annealing in Indium Arsenide Grown on Silicon
Semiconductor
Annealing is a type of heating treatment that can relieve the stresses and strains in the crystal
lattice of semiconductors. The intense heat diffuses the arrangement of atoms and rearranges
the crystal lattice. This heat treatment alters the electrical properties and can reduce
crystallographic defects in semiconductors. InAs grown on Si has a high interest to be used in
semiconductor material since it has a narrow band gap and high electron mobility. InAs and Si
both have a diamond cubic crystal structure; however InAs has a larger diamond cubic structure
than Si. The difference in size lattices between the InAs and Si limits its electrical properties
because it will cause variances in its structure. The heat treatment given to InAs grown Si did
not improve its electrical properties. There was lower mobility due to more defects in the crystal
lattice and higher sheet resistance. Since InAs has a larger diamond cubic structure than Si, InAs
has to stress and strain to grow onto the small Si crystal lattice. TEM images of the annealing
treatment suggest that the stresses in the InAs were relieved, which caused defects to form as
the crystal lattice diffused and rearranged. Any heat treatment in the fabrication of growing
InAs on Si should be avoided. Heat treatment has a negative effect on the mobility and
resistance in thin 20 nanometer InAs grown on Si.