Nano Science (Lec8 Bandgap Engineering)

Nano Science (Lec8 Bandgap Engineering) - MAE 287/EE 257 1...

Info icon This preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
MAE 287/EE 257 1
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
InSb InAs GaSb AlSb InP GaAs Ge Si SiC (6h) AlN (w) AlN (z) GaN (w) GaN (z) InN (w) InN (z) AlAs GaP AlP CdTe CdSe ZnTe CdS MgSe MgS ZnSe ZnS 10 20 30 0 10 -10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1.0 1.5 2.0 5.0 0 1 2 3 4 5 6 7 1.8 2 2.2 2.4 2.6 2.8 3 II-VI III-V (indir) III-V (dir) IV-IV Bandgap ( eV ) Interatomic Distance ( A ) Wavelength ( m ) m Bandgap Engineering : By selecting the materials with appropriate bandgap and turning the bandgap by altering the sizes of quantum structures. 2
Image of page 2
3 The bandgap increases with decreasing quantum dot size. Because of this, smaller quantum dots are expected to emit light at higher energy (lower wavelength, a blue shift) and larger dots are expected to fluoresce (emit) at longer wavelengths (red shift). 2 2 , 2 * * 3 1 1 = + ( + ) 2L g g bulk e h h E E m m
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
In natural materials, the electronic structures are defined by structures of atoms, molecules, and solids. However, we can modify the electronic structures further by controlling the sizes and dimensions to create 2D (quantum well), 1D (quantum wire) and 0D (quantum dot) structures. 4
Image of page 4
A quantum well is a potential well that confines electrons and holes to two dimensions. The effects of quantum confinement take place when the quantum well thickness becomes comparable at the de Broglie wavelength of the electrons and holes (usually smaller than ~100 nm). Quantum wells are formed in semiconductors by having a material, like gallium arsenide sandwiched between two layers of a material with a wider bandgap, like aluminum arsenide. The electronic and optical properties of such "quantum" semiconductor structures are profoundly altered from those of the bulk semiconductors. 5
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
E c Conduction Band Edge E v Valence Band Edge This band structure is different for different materials. When two materials such as GaAs and AlGaAs joined together, the band offsets between the conduction and valance bands and acts as a potential barrier to confine the electrons. 6
Image of page 6
E 0 is the band edge of conduction or valance bands. Along x and y directions, the electrons and holes are moving like a free electron but with an effective mass m*, For a QW grown along z with a width L z . The Schrodinger’s equation can be written as 2 2 0 * ( ( ) ( ) ( )) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 x y z V z x y z E E x y z m ) ( ) ( * 2 2 2 2 x E x x m x ) ( ) ( * 2 2 2 2 y E y y m y * 2 2 2 m k E x x * 2 2 2 m k E y y 7
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 2 0 2 ( ) V(z) ( ) ( ) ( ) 2 * x y z z E E E E z m z   Along z direction, the Schrodinger’s equation becomes, 2 2 2 2 0 2 * 2 * y x z k k E E E m m From the result of infinite potential well, with ) L n ( * 2 2 z 2 m E z With n=1,2,… 8
Image of page 8
The total energy E - k dispersion relation 2 2 2 2 2 2 0 z n E = E + ( ) 2 * 2 * 2 * L y x k k m m m 9
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern