Why do we need a substrate while growing?

  • Context: Undergrad 
  • Thread starter Thread starter Weimin
  • Start date Start date
  • Tags Tags
    Substrate
Click For Summary

Discussion Overview

The discussion revolves around the necessity of using a substrate in material growth processes, particularly in the context of semiconductor materials like GaN and AlN. Participants explore the implications of lattice mismatch, the choice of substrates, and the methods of material deposition.

Discussion Character

  • Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • Some participants question why the same crystal is not used as a substrate for growing materials, citing GaN grown on Al2O3 as an example.
  • Others explain that the choice of substrate depends on the specific material being grown, noting that homoepitaxy (using the same material as substrate) is possible but not always desirable.
  • One participant mentions that mismatching can be beneficial for certain applications, such as the growth of low-dimensional heterostructures like quantum dots and wells.
  • A participant emphasizes the need for a pristine surface with a specific crystallographic orientation, which may require in situ growth rather than using pre-made surfaces.
  • It is noted that lattice mismatch issues for GaN can be addressed by using a buffer layer, such as AlN, and that in some cases, lattice mismatch can create desirable strain effects in films like GaAs.
  • Another participant discusses the limitations of the Czochralsky method for growing certain materials like AlN, leading to the necessity of using substrates like sapphire for epitaxial growth.
  • There is mention of minimizing strain through the use of annealed buffer layers before growing the epitaxial film.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of substrate choice, with no clear consensus on the best practices or approaches in material growth.

Contextual Notes

The discussion highlights various assumptions about the conditions under which different growth methods are applicable, as well as the specific requirements for substrate materials in relation to the properties of the films being grown.

Weimin
Messages
38
Reaction score
0
Mismatching is the problem in growing materials. I wonder why they did not use the same crystal to grow the sample. For example, GaN is grown on Al203, why not take GaN as the seed?
 
Physics news on Phys.org
That depends on what exactly you want to grow.
It is possible to use the material you want to grow as substrate (homoepitaxy), but sometimes mismatching is not a problem, but highly welcome.
For example the growth of low dimensional heterostructures (quantum dots, quantum wells, ...) requires some mismatching to work.
 
Weimin said:
Mismatching is the problem in growing materials. I wonder why they did not use the same crystal to grow the sample. For example, GaN is grown on Al203, why not take GaN as the seed?

But in many cases, what you want is a pristine surface with a particular crystallographic orientation. If that's the case, you can't just use a pre-made surface that have been exposed to air. So you have to make the film in situ and then study it.

The lattice mismatch for GaN, for example, is mostly solved by depositing a buffer layer first such as AlN. Furthermore, in films such as GaAs, the lattice mismatch is actually desirable because it produces a strain in the film that breaks the degeneracy of the crystal, allowing for the production of spin-polarized photoelectrons.

Zz.
 
I got it, thank you.
 
Also, usually the reason for growing using a deposition method such as MBE, VPE, or CVD as opposed to the Czochralsky method is because the Czochralsky method does not work. Such is the case with AlN, since at temperatures where Al is molten nitrogen is of course a gas so Czochralsky isn't possible. Therefore, AlN wafers are simply not commercially available for epitaxial growth and you need to use a substrate such as sapphire (Al2O3) to grow AlN. However, as mentioned before, the lattice mismatch is not significant usually, and the strain can be minimized by first growing a annealed buffer layer. Then the epitaxial film is grown on the buffer layer.
 

Similar threads

Graduate Why Do Voids Form at the Thin-Film Substrate Interface After Annealing?
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Full Width at Half Maximum (FWHM) Interpretation
  • · Replies 2 ·
Replies
2
Views
5K
Undergrad Time rondeau crystals, experimental observations
  • · Replies 1 ·
Replies
1
Views
3K
Eddy currents in an Aluminum substrate PCB
  • · Replies 7 ·
Replies
7
Views
2K
Seeds Need Oxygen Before Growing - Why?
  • · Replies 13 ·
Replies
13
Views
4K
Graduate Trouble Collecting IR Spectrum of a-Si:H
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Uniform Translation of a Lattice
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Why X-ray scattering in crystalline solids is elastic?
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Higher Dimensional Spheres viz. Cubes
  • · Replies 1 ·
Replies
1
Views
2K
Chemically regenerating my auto's catalytic converter?
  • · Replies 19 ·
Replies
19
Views
10K