Semiconductor Laser Physics

Double HeterojunctionzEg2Eg2Eg1Valence band edgeConduction band edge

EcEvEg1Eg2Type IEcEvEg1Eg2EcEvType IIType IIIEg1Eg2EvEc

Evolution of the threshold current of the semiconductor lasers

Basov: Nobel prize 1964 (with Prokhorov and Townes)

Basov, Vul, Popov, Krokhin: 1957 first semiconductor laser proposal and development1961 first injection laser proposal (also Dumke 1962)

Zhores I. Alferov Herbert Kroemer The Nobel Prize in Physics 2000"for developing semiconductor heterostructures used in high-speed- and opto-electronics"

III-V semiconductor grown on Ge

Lattice-matched InGaAs/AlInAs

Molecular Beam EpitaxyNeeds UHV 10-11 Torr , high-purity elemental materials, right temperatureA. Cho, Bell Labs

Growth rate 1 m/hr or 1 atomic layer in 1 sec

Reflection High-Energy Electron Diffraction (RHEED)

Metal-Organic Chemical Vapor Deposition (MOCVD)

Growth rate 2-4 m/hr

Materials for semiconductor lasers

GaAs/AlxGa1-xAs; GaxIn1-xAsyP1-y/AlxIn1-xAs on InP; InAs1-xSb/AlGa1-xSb on GaSb

Visible-UV range

Laser Diode

Laser waveguidesVertical confinementLateral confinementGain-guidedIndex guided: ridges, ribsBuried heterostructure lasers

Ridge laser

H-field of the TM00 mode at 8.85 mumIn QCLs you can cut the ridge through the active region: strong guiding

H-field of the TM02 mode at 8.85 mum

Modes: longitudinal and transverse

Buried heterostructure laser

2743 B ridge

3032 C device 250K

DFB lasers

Vertical Cavity Surface-Emitting Laser

Large distance between cavity modes: single-mode laser Circular beam shape Low threshold and power consumption 2D laser arrays Wafer-scale testing Ultrafast modulation

Edge-emitting laserVCSEL

For long wavelength laser based on InGaAsP/InP: index contrast is too low, need too many layers, the device is too resistive as a result

Current spreading, many transverse modes -> need confinement for current and for the EM field

Oxidized aperture VCSEL

Oxide apertureHuffaker et al. APL 1994Problems: different thermal expansion coefficient, strain, bad control, non-planar technology

Phase-shifting mesaLu et al., APL2004

Oxide aperture and phase-shifting mesaAhn et al. APL 2005

From bulk materials to heterostructuresAdd slowly varying perturbation U(r) to the bulk Hamiltonian H0

(b) Seek the solution as a product zf(z) slowly varying envelope function(c) Assume that un0(r) and kx,y are the same in each layer(d) Replace kz with and solve the resulting differential matrix equation for the column-vector f(z)Advantage of the method: everything is expressed in terms of several parameters that can be measured: Eg, SO, meff(k = 0)