10 100 10000

100

200

300

400

500

1100

1200 I

I

ISh

p-doped

I

Uni. Tokyo, F

F - Fujitsu Lab.I - Ioffe Phys.-Tech. InstituteM - University of New MexicoT - University of TexasW - University of WuerzburgSh- University of Sheffield

T0 (

K)

Jth (A/cm2)

T IMM

MF

T

FF

T W WF

T

T

IT

T

T

M

recent results

Quantum Dot Lasers (1.3m)

Low Jth achieved but T0 remains finite around RT

High T0 in p-doped QDs at expense of higher Jth

T0 in all p-doped lasers is dropping down 60-70 K just above 60oC

Our results show this is due to: changes in carrier confinement and transport due Columbic attraction of extra holes a decrease of Jth with increasing T until thermal equilibrium point together with increasing Auger process explain high T0 in the p-doped QD lasers

Nicolas Masse, Igor Marko, Stephen Sweeney, Alf Adams

GaInNAs Avalanche Photodiodes (APDs)

• Avalanche Photodiodes are highly sensitive and low noise solid-state optical detectors with internal gain

– Equivalent to photo-multiplying tubes• Silicon is the material of choice for

<1.06m• For telecom wavelengths most III-V

materials are not suitable• We are investigating whether GaInNAs

will be useful for application in APDs• Preliminary Results

– Increasing Nitrogen content increases Breakdown voltage

– Reduction in tunnelling compared to InGaAsP

Reverse bias voltage (V)

0 5 10 15 20 25

Cu

rren

t (A)

1e-12

1e-11

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

InGaAsPEg=0.992eV

GaAs

Eg=1.087eV

Dark Current Measurement

Increase in Dark current due to tunnelling

0% Nitrogen

h

Large Electric field

hole

Conduction band

Valance band

electron

James Chamings, Alf Adams, Stephen Sweeney

Laser Biosensors

Feasibility of an optical biosensor based on DFB laser technology that makes use of the evanescent field in the outer layers of a semiconductor waveguide

Adding layers toa semiconductor waveguide changes the effective index of the guide, causing a shift in wavelength of the propagating modes.

New layer

nc

ns

ng

nc

ns

ng Field Strength (E(y))

λ1

λ2

We hope to observe a change in wavelength of the DFB laser when alayer of biological molecules e.g. proteinsadsorbs to the gold surface of the device.

Later on we will try measuring the interference pattern between a sensing and a reference laser, and modifying the device surfaces to be analyte-specific to a wide variety of compounds.

t

Adsorbtion

Desorbtion

Δλ

A major goal will be thedetection of layer formationIn real time.

Jo Coote, Stephen Sweeney, Sub Reddy

Diamond Anvil Cell (DAC)

High Pressure Physics

High pressure He-gas system (up to 1.2 GPa)

Laser Window

gas

Currently developing a Sapphire ball anvil cell for electrical and

optical measurements up to 4GPa

Andy Prins, Shirong Jin, Gary Strudwick, Alf Adams, Stephen Sweeney

Extended Temperature Optoelectronics (ETOE)

Igor Marko, Stephen Sweeney, Alf Adams

• £1.7M 30 month DTI sponsored project to produce optoelectronic devices operating to high temperature

• Will facilitate Fibre-To-The-Home networks

• Large power savings ~80% due to lower cooling power (good for the environment!)

Temperature (K)0 50 100 150 200 250 300

No

rma

lise

d t

hre

sh

old

cu

rre

nt

0

5

10

15

20

1.3m InGaAsP1.5m InGaAs1.3m AlGaInAs1.5m AlGaInAs

New Al-containing laser materials have lower threshold currents and improved thermal stability

Applications

gas sensing

medical

free space comms

-1 0 1 2 3 4 5 6 7 8 9

0.8

1.0

1.2

1.4

1.6

2.18m 2.11m 2.37m

Nor

mal

ised

thr

esho

ld c

urre

nt

P (kbar)

GaInAsSb Type I QWs

2 - 3 μm

Sb-based Type II ‘W’ Lasers

3 – 4.2 μm

Pressure dependence of threshold current yields info on loss processes.

P »» Eg

Temperature dependence of the spontaneous emission emitted during operation also helps analyse loss processes. Results used to further develop these devices.

Mid-infrared Laser Characterisation (~2-10 μm) Kevin O’Brien, Stephen Sweeney, Alf Adams, Ben Murdin

1.3m laser on GaAs basis to fabricate VCSELS for Metronet communications

Spectroscopic results on the VCSELs:

GaAsSb laser (devices and spectroscopy)

Interesting material property: type I or type II

© Pacific Broadband Networks - Media Release

Ith strongly temperature dependentnon-radiative recombination

0

500

1000

1500

2000

60 110 160 210 260T (K)

Cu

rren

t d

en

sit

y (

Acm

-2)

JthJrad

0 20 40 60 80 100

0

4

8

12

16

20

24

E

(m

eV

)

I/Ith (%)

GaAsSbInGaAsP

T=260K

Study carrier recombination:

-

+

Large shift of emission in both working device (spontaneous emission) as well as wafer (PL)

type II

0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.60

100

200

300

400

500Room temperature PL on GaAsSb VCSEL

18/11/05

x0.002

PL edge PL front x0.2

PL

(a.u

.)

Energy (eV)

Konstanze Hild, Stephen Sweeney, Igor Marko, Gunnar Blume, Jeff Hosea

Using:PressureLow temperatureLife time measurements