Understanding Sn-seeded InSb nanowire growth

Abstract

III-Sb semiconductor nanowires have drawn a lot of attention because of their many promising applications, such as thermoelectric generation, low power high efficient electronics and quantum transport. Gold as a catalyst seed particle has been dominating for many years assisting nanowires growth. However, gold is incompatible with silicon-based electronics, which is dominating today. Therefore, finding metals alternative to gold as catalyst seed particles for III–V semiconductor nanowire growth is necessary. Sn was chosen as a promising seed particle for InSb nanowires growth.

The most commonly used bottom - up method is the Vapor - Liquid - Solid (VLS) mechanism. This project consisted of both experimental and theoretical components, with the aim to develop the growth of InSb semiconductor nanowires using Sn droplets and Metal Organic Chemical Vapour Deposition (MOCVD). The composition of the Sn seeded InSb nanowires (including the seed particle) were determined by X-ray energy dispersive spectroscopy (XEDS). The morphology was characterized by scanning electron microscopy (SEM). Sn-seeded InSb nanowires growth was also discussed from a thermodynamic viewpoint using the phase diagram.

The optimized growth temperature was found to be 420C. The growth rate is low. Due to sample edge effects, the morphology of the nanowires (excluding the seed particle) is different between center and edge of the sample. The resulting InSb nanowires are much thicker (450 nm) and shorter (450 nm) compared to gold-seeded InSb nanowires. The nucleation and polarity of Sn-seeded InSb nanowires are more affected by V/III ratio than temperature. Particle size is strongly influenced by TMIn flow. The Sb amount is a key factor to control the morphology of InSb nanowires. We conclude that Sn-seeded InSb nanowires growth results in self-seeded (In) seeded InSb nanowires growth. The reasons are: 1). The seed particle size increases much during nanowires growth, from about 150 nm to 403 nm; 2). There is no significant effect on particle size with smaller seed particles growth; 3). XEDS measurements show that no Sn is detected. Mass transport modeling fits the experimental data of TMIn series much better than TMSb series. Further experiments on InSb nanowires growth without Sn seed particles verified that Sn-seed particles help nucleation and affect the InSb NWs growth.

Popular Abstract

In daily life, crystals are very commonly seen, for example snowflakes, ice, diamonds, and table salt. Their atoms or molecules are arranged in highly ordered structures. However, there are normally some defects inside the crystal, which make the crystal structure not perfect. Semiconductors are crystalline or amorphous solids. For example silicon is a very common semiconductor material. The III-V semiconductors contain two elements, one from the periodic table’s 13th column (III) such as aluminum, gallium, or indium, and one from the 15th column (V), such as phosphors, arsenic, or antimony. When these two elements are combined together, they form for example InAs, GaSb, and InSb. As its name implies, the semiconductor’s ability to conduct current can be controlled. This property makes them very useful. For example, an electronic chip and the transistors on it, and LEDs are all made of semiconductor material.

We want to make for example the electronics inside the computer or phone small but highly efficient. Thus, we want to pack as many components as possible on the chip. So we make things as small as possible. For this purpose we study semiconductor nanowire materials. The nanowire is an example of one dimensional nanostructure. The In and Sb atoms are carried as metal-organic reactants in the gas phase. After decomposition of these reactants, the In and Sb atoms as building blocks form a crystal structure (solid phase) themselves that arranges into a cylindrical shape (20-60 nm in diameter and micrometer in length). In order to increase the growth rate, catalyst seed particles (Au or Sn, which are not consumed during nanowire growth) are formed on substrate before nanowire growth. The nanowire growth takes place at the interface of seed particle and the solid nanowire. Certain conditions are needed for this growth for example, pressure, temperature, concentration, flow rate, time and so on. The figure shows one of the obtained InSb nanowires.

How to see these nanowires as they are so tiny? The answer is electron microscopy. Using this tool one can check the morphology or structure of nanowires down to atomic resolution. Each atom will have its specific electron shell energy which can be used to identify that atom. A source in the electron microscopy can generate electron beams with certain energy in the range of 10 to 300 keV. When the electron beam shoots on the sample with nanowires, high energy electrons from the incident beam will interact with the electrons inside the nanowires. Thus some electrons will be knocked out of the nanowires and some incident electrons will be back or forward (with energy loss or not) in many different angles. Detectors in the electron microscopy will collect these electrons and give the feedback as images. Thus we could see how the nanowires look like and their atomic structure and composition and so on using electron microscopy.

• author: Zhang, Hengfang
• supervisor: Jonas Johansson
• organization: Department of Physics; Solid State Physics
• course: FYSM60 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Science General
• language: English
• id: 8913928
• date added to LUP: 2017-06-12 11:53:51
• date last changed: 2017-06-29 15:02:06