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Quantum Well-Laser Diodes with Output Characteristics Stabilized by Inherent Temperature-Induced Pressure

IP.com Disclosure Number: IPCOM000118457D
Original Publication Date: 1997-Feb-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 105K

Publishing Venue

IBM

Related People

Daetwyler, K: AUTHOR [+2]

Abstract

Operating parameters of laser diodes, such as threshold current, optical output power, differential efficiency, and emission wavelength are known to depend sensitively on temperature and mechanical strain. Since the gain maximum in quantum well lasers is at band edge and the index of refraction is dominated at the absorption edge, laser parameters usually track with the bandgap energy 'E' sub g as it changes with temperature T and pressure p.

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This is the abbreviated version, containing approximately 52% of the total text.

Quantum Well-Laser Diodes with Output Characteristics Stabilized
by Inherent Temperature-Induced Pressure

      Operating parameters of laser diodes, such as threshold
current, optical output power, differential efficiency, and emission
wavelength are known to depend sensitively on temperature and
mechanical strain.  Since the gain maximum in quantum well lasers is
at band edge and the index of refraction is dominated at the
absorption edge, laser parameters usually track with the bandgap
energy 'E' sub g as it changes with temperature T and pressure p.

      This disclosure uses the pressure induced by thermal expansion
to counteract the impact of temperature changes in laser diode
structures.  That is, temperature effects will be compensated in an
ideal way by a reacting pressure when the net temperature change of
'E' sub g is zero:
                                  eqno  (1)
  <'dE' sub 'g' ('T,p')> over <'dT'>%%%=%%%
  <vardelta 'E' sub 'g'> over <vardelta 'T'> lor  sub 'p'%%%
  +%%%<vardelta 'E' sub 'g'> over <vardelta 'p'> lor  sub 'T'%%
  multiply  %%<vardelta 'p'> over <vardelta 'T'>%%%=%%%0.

      This implies that the differential expansion between two
adjacent layers of material is large, that is, a large-expansion
layer is surrounded by a layer with low (or zero for best results)
thermal expansion.

      The principle of the proposal will be demonstrated at
InGaAs/AlGaAs quantum well ridge waveguide lasers composed of
direct-gap semiconductors.  The temperature coefficient of the
bandgap energy of the active InGaAs quantum well layer has a negative
sign, whereas the sign of the pressure coefficient of the bandgap of
the same layer is positive.  The reversed signs of the temperature
and pressure coefficient are characteristic for direct-gap
semiconductors and crucial for achieving zero energy gap increase
with increasing temperature, i.e., for realizing this invention at
all.  The calculation shows that in order to satisfy equati...