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SUMMARY:Porous nitride semiconductors for novel light sources - Rachel Oli
 ver (DMSM)
DTSTART:20250226T161500Z
DTEND:20250226T171500Z
UID:TALK224815@talks.cam.ac.uk
CONTACT:Lucas Sá
DESCRIPTION:Porous semiconducting nitrides are effectively a new class of 
 semiconducting material\, with properties distinct from the monolithic nit
 ride layers from which devices from light emitting diodes (LEDs) to high e
 lectron mobility transistors are increasingly made. The introduction of po
 rosity provides new opportunities to engineer a range of properties includ
 ing refractive index\, thermal and electrical conductivity\, stiffness and
  piezoelectricity. Quantum structures may be created within porous archite
 ctures and novel composites may be created via the infiltration of other m
 aterials into porous nitride frameworks.  \nA key example of the applicati
 on of porous nitrides in photonics is the fabrication of high reflectivity
  distributed Bragg reflectors (DBRs) from alternating layers of porous and
  non-porous GaN.  These reflectors are fabricated from epitaxial structure
 s consisting of alternating doped and undoped layers\, in which only the c
 onductive\, doped layers are electrochemically etched. Conventionally\, tr
 enches are formed using a dry-etching process\, penetrating through the mu
 ltilayer\, and the electrochemical etch then proceeds laterally from the t
 rench sidewalls.  The need for these trenches then limits the device desig
 ns and manufacturing processes within which the resulting reflectors can b
 e used. We have developed a novel alternative etching process\, which remo
 ves the requirement for the dry-etched trenches\, with etching proceeding 
 vertically from the top surface through channels formed at naturally-occur
 ring defects in the crystal structure of GaN (see Figure). This etch proce
 ss leaves an undoped top surface layer almost unaltered and suitable for f
 urther epitaxy.\nThis new defect-based etching process provides great flex
 ibility for the creation of a variety of sub-surface porous architectures 
 on top of which a range of devices may be grown.  Whilst DBR structures en
 able improved light extraction from LEDs and the formation of resonant cav
 ities for lasers and single photon sources\, recent development also sugge
 sts that thick\, sub-surface porous layers may enable strain relaxation to
  help improve the efficiency of red microLEDs for augmented reality displa
 ys.  Meanwhile\, the option of filling pores in nitride layers with other 
 materials provides new opportunities for the integration of nitrides with 
 emerging photonic materials\, such as the hybrid-perovskite semiconductors
 \, with perovskites encapsulated in porous nitride layers demonstrating gr
 eatly improved robustness against environmental degradation.\n
LOCATION:Small Lecture Theatre\, Cavendish Laboratory\, J.J. Thomson Avenu
 e
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