We continue to develop resources related to the COVID-19 pandemic. See COVID-19 initiatives on Appropedia for more information.

Difference between revisions of "Semiconductor recycling plant case study of GaAs photovoltaic manufacturing - case study"

From Appropedia
Jump to navigation Jump to search
Line 17: Line 17:
 
VGF growth works by placing high purity arsenic and gallium in an enclosed quartz ampoule with a crystal of GaAs.  The arsenic and gallium are melted, and then brought into contact with the GaAs crystal.  When cooled slowly, a single crystal of GaAs is formed.  The single crystal formed has many of the same impurities as LEC growth crystals, which restricts the utility of the crystals.
 
VGF growth works by placing high purity arsenic and gallium in an enclosed quartz ampoule with a crystal of GaAs.  The arsenic and gallium are melted, and then brought into contact with the GaAs crystal.  When cooled slowly, a single crystal of GaAs is formed.  The single crystal formed has many of the same impurities as LEC growth crystals, which restricts the utility of the crystals.
  
 +
 +
[[File:Manufacturing process of GaAs.png|thumb|left|Manufacturing process of GaAs and other semiconductors with the waste products produced]]
  
 
==Thin Film Growth==
 
==Thin Film Growth==

Revision as of 15:43, 30 September 2011

Asi.png This page was part of a project for MY3701 -- an MTU class on semiconductors.

This page is now open edit -- please fix mistakes or feel free to leave comments using the discussion tab.



Introduction

Gallium arsenide (GaAs) is a semiconductor material that is used in a wide variety of applications ranging from circuits to solar cells. Solar cell of GaAs can be produced using both bulk and thin film growth methods.


Bulk Growth

There are two common ways to produce GaAs using bulk growth, Liquid-Encapsulated Czochralski (LEC) growth, and Vertical Gradient Freeze (VGF) technology. [1]

LEC growth is accomplished by melting high-purity arsenic and gallium in a high temperature vessel, and slowly cooling to produce a single crystal. The GaAs crystal produced using this method however has some impurities such as significant levels of carbon, and numerous dislocations. These impurities cause the semiconductor to be unusable for some applications.

VGF growth works by placing high purity arsenic and gallium in an enclosed quartz ampoule with a crystal of GaAs. The arsenic and gallium are melted, and then brought into contact with the GaAs crystal. When cooled slowly, a single crystal of GaAs is formed. The single crystal formed has many of the same impurities as LEC growth crystals, which restricts the utility of the crystals.


Manufacturing process of GaAs and other semiconductors with the waste products produced

Thin Film Growth

Thin films of GaAs have many advantages over large single crystals of GaAs when it comes to being used in solar cells. Thin films lack some of the impurities found in large crystals, and are capable of being used without requiring extensive slicing. The rest of the case study will be dedicated to thin film GaAs semiconductors.

The most common thin film growth methods for producing GaAs films are Vapour Phase Epitaxy (VPE), Metalorganic Chemical Vapour Deposition (MOCVD), and Molecular Beam Epitaxy (MBE).


Plausibility of Recycling

Amount of material in a typical cell = 3100 g/m2

Peak Power = 272.8 W/m2

Amount of material per Watt Peak = 11.4 g/Wpeak[2]


Metalorganic Chemical Vapour Deposition (MOCVD)

Material utilization efficiency = 30%[3]

Waste material rate MOCVD = 2170 g/m2 and 7.98 g/Wpeak


Molecular Beam Epitaxy

Material utilization efficiency for Ga = 40-70%

Material utilization efficiency for As = 10-20%

Average Material utilization efficiency = 35%

Waste material rate MBE = 2015 g/m2 and 7.41 g/Wpeak


Forms of Collection of Waste

References

  1. R.L. Adams, Growth of high purity GaAs using low-pressure vapour-phase epitaxy, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 395, Issue 1, 1 August 1997, Pages 125-128, ISSN 0168-9002, 10.1016/S0168-9002(97)00624-4. (http://www.sciencedirect.com/science/article/pii/S0168900297006244) Keywords: Low-pressure vapour-phase epitaxy; LPVPE; GaAs
  2. http://www.spacequest.com/products/SP-X.pdf
  3. http://www.bnl.gov/pv/files/pdf/art_168.pdf