Tag Archives: Quantum Wells

Quantum Well: InP-InGaAsP-InP

Quantum wells are widely used in optoelectronic and photonic components and for a variety of purposes. Two materials that are often used together are InP and InGaAsP. Two different models will be presented here with simulations of these structures. The first is an InP pn-junction with a 10 nm InGaAsP (unintentionally doped) layer between. The second is an InP pn-junction with 10 nm InGaAsP quantum wells positioned in both the positive and negative doped regions.

Quantum Well between pn-junction

quantum well

The conduction band and valence band energies are depicted below for the biased case:

quantum well2

The conduction current vector lines:

qwell1

ATLAS program:

go atlas
Title Quantum Wells
# Define the mesh
mesh auto
x.m l = -2 Spac=0.1
x.m l = -1 Spac=0.05
x.m l = 1 Spac=0.05
x.m l = 2 Spac =0.1
#TOP TO BOTTOM – Structure Specification
region num=1 bottom thick = 0.5 material = InP NY = 10 acceptor = 1e18
region num=3 bottom thick = 0.01 material = InGaAsP NY = 10 x.comp=0.1393  y.comp = 0.3048
region num=2 bottom thick = 0.5 material = InP NY = 10 donor = 1e18
# Electrode specification
elec       num=1  name=anode  x.min=-1.0 x.max=1.0 top
elec       num=2  name=cathode   x.min=-1.0 x.max=1.0 bottom

#Gate Metal Work Function
contact num=2 work=4.77
models region=1 print conmob fldmob srh optr
models region=2 srh optr
material region=2

#SOLVE AND PLOT
solve    init outf=diode_mb1.str master
output con.band val.band e.mobility h.mobility band.param photogen opt.intens recomb u.srh u.aug u.rad flowlines
tonyplot diode_mb1.str
method newton autonr trap  maxtrap=6 climit=1e-6
solve vanode = 2 name=anode
save outfile=diode_mb2.str
tonyplot diode_mb2.str
quit
Quantum Well layers inside both p and n doped regions of the pn-junction
Structure:
qwell3
Simulation results:
qwell2
#TOP TO BOTTOM – Structure Specification
region num=1 bottom thick = 0.25 material = InP NY = 10 acceptor = 1e18
region num=3 bottom thick = 0.01 material = InGaAsP NY = 10 x.comp=0.1393  y.comp = 0.3048
region num=4 bottom thick = 0.25 material = InP NY = 10 acceptor = 1e18
region num=2 bottom thick = 0.25 material = InP NY = 10 donor = 1e18
region num=6 bottom thick = 0.01 material = InGaAsP NY = 10 x.comp=0.1393  y.comp = 0.3048
region num=2 bottom thick = 0.25 material = InP NY = 10 donor = 1e18

The Quantum Well

What is a Quantum Well

Optical Integraded devices are normally built with the consideration that the device size will be large compared to the wavelength of the beams in the system. When however, the device size is reduced to a size of the same order of magnitude as the wavelength of light in the system, unique properties can be observed. The class of device that operates under the unique properties of this arrangement is the “quantum well.”

 

Uses of Quantum Wells

Quantum wells may be integrated to other optical and opt-electronic integrated circuits. Uses of quantum wells include improved lasers, photodiodes, modulators and switches.

 

Building a Quantum Well

A quantum well structure features one or more very thin layers of narrow bandgap semiconductor material, interleaved with layers of wider bandgap semiconductors. The thickness of the layers in a quantum well are typically 100 Angstroms or smaller. Quantum wells with many layers are termed a “Multiple Quantum Well” (MQW) structure and quantum wells with only one layer are termed a “Single Quantum Well (SQW) structure. A typical MQW structure may have around 100 layers. The GaAs-AlAs material system or GaInAsP are common choices for materials in quantum well structures.

quantumwell1

Superlattice Structure

A superlattice structure is a term for a case in whic a multiple quantum well structure is built with barrier wals that are thin enough that electrons are able to tunnel through the structure.

 

The Quantum Well and Quantum Dot

qwell1

The quantum well reduces the separation between an electron and hole in a semiconductor, altering the wavefunction and allowing a strong exciton bonding effect at room temperature. The semiconductor laser results from this process. Wave functions in the well are shown to the right.

When a field is applied across the well, this can result in the tilting of the wells. This can reduce the effective band gap of the material. The process of tilting the wells the alter the band gap is called the Quantum Confined Stark Effect.

qwell3

 

Quantum wells are generally understood in two dimensions. The conduction band is forced to be closer the valence band. When this is done in three dimensions to create a small box, where this squeezing effect can be emulated in all dimensions, this is termed a Quantum Dot. A Quantum Dot it turns out is highly effective at producing a high level of energy and as a result there is a high probability that it works as a coherent light source (laser). Quantum dots are readily used today, however since the process of fabrication employs the use of defects in a material to create a quantum dot, the coherency of the light produced is not perfect. Quantum dots are used in data centers for light transmission at a distance of meters. Quantum dots remain a low cost and reasonably efficient light transmission source for small distances. One reason for the low cost of quantum dots is that they can be grown on silicon wafers. A quantum well is not easily (highly unreliably, but perhaps not impossible) grown on Silicon wafers. The issue that arises with quantum wells when being grown on silicon wafers is that the size of atoms in the wafers and thereby the lattice constant is not readily compatible.