Lateral Composition Modulation in InAs/GaSb Superlattices: Nanometer Sized Quantum Wires

Donna W. Stokes DMR 0237811One of the objectives of this research is to understand the structural properties of the nanowires formed by lateral composition modulation (LCM) in InAs/GaSb

superlattices.

Figure 1 show a diagram of the 3D structure of the InAs/GaSb nanowire array as seen in a scanning tunneling microscopy image of the sample. 100-150 nm InAs wire-like structures have been observed.

An X-ray diffraction reciprocal space map, Fig. 2a, was used to determine the LCM wavelength, composition and strain state of the layers. Addition XRD lines scans, shown in Fig. 2b and 2c, were performed and this data was modeled to determine the composition of the layers which were determined to be InAs0.88Sb0.12 and GaAs0.09Sb0.91 due to contamination/segregation. This alters the strain state of the layers with respect to that of the InSb interface, therefore, nanowire structures are formed for the “InAs” layers despite a small misfit. We have determined that this new strain relationship is largely responsible for the nanowire formation. We believe that with proper design of the interfacial bonding, self-assembled nanostructures can be grown in material systems with small misfit, which would otherwise be impossible.

Fig. 2. (a) X-ray reciprocal space map around the (24) reciprocal lattice points of the nanowire sample. (b) Qx scan at Qz = 3.9887.

(c) Qz scan at Qx=2.00. The inset in (c) is a (004) Qz scan at Qx=0.

Dots – experimental data; lines – simulation.

University of Houston

Fig. 1. A reconstructed 3D structure of the InAs/GaSb nanowire array.

1.98 1.99 2.00 2.01

3.9

4.0

4.1

4.2

3.8 3.9 4.0 4.1 4.2 4.3

3.9 4.0 4.1

Log

Inte

nsity

(ar

b. u

nit)

Qz (r.l.u.)

(0,0)

(0,-2)

(0,2)(0,4)

(0,-4)(0,6)

Qx=2.00(c)

Qz (r.l.u.)

Inte

nsity

(0,0)(0,-2) (0,2)

(004)Sub

1.98 2.00 2.02

Inte

nsity

(ar

b. u

nit)

Qx (r.l.u.)

(2,0)(-2,0)

(-4,0) (4,0)

(0,0)Qz=3.9887(b)

Qx (r.l.u.)

Qz

(r.l.

u.)

(a)

b

c(224)

]110[

]001[

]101[

Education and Outreach:During the summer 2004 Houston Independent School District (HISD) high school mathematics teacher, Katrina Cushenberry, worked in the PI’s laboratory on a project based on nanoscale technology and how it will affect our future. During her nine weeks tenure, she learned numerous techniques used for analyzing nanoscale semiconductor materials, such as infrared spectroscopy and photoluminescence. She was also involved in data analysis using programs such as Origin. This experience will allow Ms. Cushenberry to inspire her students to pursue careers in the areas of Science and technology.

Members of my group also served as judges for the Houston Engineering and Science Fair in Houston, Texas. I also served as judge for the Science Fair at HISD’s Peterson Elementary.

The PI poses in front of a second grader’s science project entitled “What is Static Electricity?” at Peterson Elementary’s Science Fair.

Lateral Composition Modulation in InAs/GaSb Superlattices: Nanometer Sized Quantum Wires

Donna W. Stokes DMR 0237811University of Houston

Ms. Cushenberry assists the PI with alignment of a sample for infrared spectroscopy.