Current-injection lasing in T-shaped GaAs/AlGaAs quantum-wire lasers

1
Current-injection lasing in T-shaped GaAs/AlGaAs
quantum-wire lasers
Shu-man Liu1, Masahiro Yoshita1, Makoto Okano1,
Hidefumi Akiyama1,2, Loren Pfeiffer2, and Ken
West2
1Institute for solid State Physics, University of
Tokyo,CREST and JST, Chiba 277-8581, Japan2Bell
Laboratories, Lucent Technologies, Murray Hill,
New Jersey 07974, USA
Results
Introduction

Current-Voltage-Power Characteristics
Emission spectra and images

• Quantum-wire lasers are expected to operate
  efficiently with low injection currents.
  Intensive experimental efforts have been made to
  verify and understand low threshold currents in
  quantum-wire lasers.
• Nevertheless, physics arguments on low
  threshold current in quantum-wire lasers are
  still unclear, because threshold currents are
  determined not only by the optical and material
  properties, but also by the design of optical
  waveguide and cavity, and the electrical
  properties of the laser devices.
• Further experiments are necessary on
  quantum-wire laser samples with high
  controllability in material, optical, and
  electrical structures.

Our Research

• Lowest threshold current 0.27 mA
• Threshold current density per single-wire
  7x105/cm
• External differential quantum efficiency 12
• Single-mode output power at 1 mA bias current
  0.13 mA
• Turn-on voltage(30-70 K) 1.55 V
• Front facet R96.8, T1.0, Abs 2.2
• Rear facet R98.1, T0, Abs 1.9
• Estimated internal loss 0.32.

• We demonstrate low-threshold single-mode lasing
  in 20-period T-shaped quantum-wire lasers with
  high material quality and a new efficient current
  injection scheme.

• Emission from the T-wires dominates the EL
  spectra.
• No EL or lasing was observed from stem wells,
  indicating effective current confinement in the
  arm well.
• Single-mode lasing was obtained at 1.555 eV from
  the lowest subband transition.
• Single-mode lasing has been similarly observed
  at the cryostat temperatures between 30 and 70 K.
• Near-filed patterns show tight optical
  confinement.

Experimental
Schematic structure of a T-shaped quantum-wire
laser sample
Gain-Photon energy-Current Characteristics

• The T-wire laser structures were fabricated by a
  cleaved-edge overgrowth method with MBE. After
  MBE growth, the upper (001) layers were partially
  etched away, and AuBe/Au and Ni/Ge/Au/Ni/Au were
  deposited as the p- and n-type ohimic contacts,
  respectively.
• Cavity facets of some lasers were
  high-reflection coated by 50-nm Au-layers on the
  front and 300 nm on the rear after deposition of
  70-nm SiO2 insulating layer,

• We extracted the absorption spectra from the
  depth of the modulation of the nascent
  Fabry-Perot modes in the amplified spontaneous
  emission spectra by Hakki-Paoli method.

Summary and Viewpoint

• We have presented a low-threshold
  current-injection laser using 20 periods of
  T-shaped GaAs/AlGaAs quantum wires as gain medium
  with a simple current-injection scheme.
• We have demonstrated c.w. single-mode lasing at
  1.555 eV with threshold current of 0.27 mA and
  differential quantum efficiency of 12 at 30K.
• By a similar current injection scheme, a
  threshold current of several tens ?A is expected
  to be achieved in a single-wire laser.
• This work was partly supported by a Grant-in-aid
  from the Ministry of Education, Culture, Sports,
  Science, and Technology, Japan.

Scanning photoluminescence spectra measured at
5K. Excitation laser spot size was 0.8 ?m in
diameter.

• Currents are expected to be confined in the
  single arm well by this arm-arm injection scheme.
• Emission energies of various components can be
  distinguished by the microPL spectra..