funded by the european union - ga 737089 kick-off … by the european union - ga 737089 kick-off...

Funded by the European Union - GA 737089 1 Kick-Off Meeting, Barcelona, Jan 17-18, 2017

ChipScope project kick-off meeting

GaN Nano- and MicroLED Technology

Hutomo Suryo Wasisto and Andreas Waag

Institute of Semiconductor Technology (IHT),

Laboratory for Emerging Nanometrology (LENA), Technische Universität Braunschweig,

Braunschweig, Germany

E-mail: [email protected], [email protected]

Funded by the European Union - GA 737089 2 Kick-Off Meeting, Barcelona, Jan 17-18, 2017

mailto:[email protected]�






Andreas Waag - Braunschweig University of Technology – page 3

Braunschweig University of Technology Technische Universität Braunschweig (TUBS)

1745 founded as Collegium Carolinum 1 University

6 Faculties

120 Institutes

1.800 Scientists 20.000 Students (BS: 250.000 citizens)

65 Mio. Euro External Research Funding 250 Mio. Euro Overall Budget largest portfolio of engineering BA/MA programs

in northern Germany member of :


Institut für Halbleitertechnik

(Fündling)

headcount ca. 50

Junior Reserach Group OptoSense (Wasisto)

Dept. Electrical Engineering


Epitaxy Competence Center @ TUBS

in collaboration with

GaN Technology / Foundry Services.


Epitaxy Competence Center - Infrastructure

• 2 cleanrooms each with ~120 m² labspace • Infrastructure: Epitaxy – Analysis - Processing

ALD, 3xMOCVDs, ICP etching, Photolithography, Nanoimprint, FESEM, CL, PL, AFM, Sputter systems, PVD …

Sentech dry etcher for Si and nitrides

AIXTRON G3 2600HT

Thomas Swan 3x2“ FT

Tescan Mira with Gatan MonoCL

soon: Laser-Lift-Off, FIB-SEM, SIMS, TEM…

Laboratory for Emerging NAnometrology

our mission:

precise measurement at the nanoscale

Speaker: Waag

GRK


GaN LEDs: The basis of „Solid State Lighting“

Efficiency: <1% 4-5% 40-50%

Century:

Candle light bulb LED


Principle of light production in a LED

conduction band

valence band

light

Electronic transition between 2 energy levels produces photons

The energy difference determines the color of the LED

Electrons current in

current out

Ene

rgy

x

LED


Principle of light production in a LED

conduction band

valence band de

plet

in

regi

on

Electronic transition between 2 energy levels produces photons

The energy difference determines the color of the LED

Electrons electron current

in

hole current in

Ene

rgy

x

LED

n-type p-type

band

gap


Electronic bands in a high power InGaN/GaN LEDs

InGaN/GaN/AlGaN LED with electron blocking layer (EBL) top: „flat band conditions“ (during current flow) bottom: including band bending due to doping Typical ingredents: p-and n-doped (Al)GaN confinement layers multiple quantum wells electron blocking layer p-type GaN always on top (low quality) !

total width about 1 µm


The dimensions in case of InGaN/GaN LEDs…

Top 10 µm = GaN buffer + LED structure

substrate thickness = 300 – 1000 µm

1 µm

sapphire wafer dimensions = 2,4,6 inch

always „p-type on-top“


White GaN-LED

Quelle: OSRAM OS 2003

white = yellow + blue

LED emission

emission of the phosphor

yellow emitting phosphor

blue emitting LED chip


Pacakging of LEDs

LED = Light Emitting Diode

SMD = surface mounted device

Through Hole Mounting


Materials for optoelectronics : lattice matching necessary

lattice constant [A]

band

gap

[eV

]

wav

elen

gth

/nm

)

Bergbauer , Strassburg et al, Physik-Journal 2011


The „Green Gap“ : internal qauntum efficiency

in th egreen spectral range, the efficiency of both nitride and phosphide LEDs suffers: no high efficiency green LEDs / laser diodes

(might change in the next future)


Metalorganic Chemical Vapor Phase Epitaxy (MOVPE)

60 wafers, 2 inch diameter 400 LEDs per wafer 24.000 LEDs per growth run per MOVPE


MOCVD von AlGaN: the concept of MO chemistry

Andreas Waag | Lichttechnik 7| Seite 18

Nakamura 1991 P= 200-1000 mbar

high temperatures lead to convection

TMGa = Trimethyl-Gallium TMAl = … Aluminum TMIn = … Indium


Moore´s Law in Solid State Lighting

microelectronics smaller transistors faster transistors more functionality per chip more logic units

solid state lighting

higher efficiency

higher currents

larger light emitting area

more optical power per chip more photons

Semiconductor Technology

from better efficiency to smart production / cost efficiency

since efficiency is almost in saturation, we need to change our perspective:


„Moores Law“ in Solid State Lighting“ [Haitz, Tsao, Phys. Status Solidi A 208(2011)1]

from better efficiency to smart production / cost efficiency

since efficiency is almost in saturation, we need to change our approach:

GaN


DROOP

low current densities increase efficiency, but also increase cost per photon

DROOP = reduction of efficiency with increasing current density

Quelle: OSRAM OS

B.Hahn (OSRAM OS) DOE Workshop 2016


The nanorod approach Core-shell geometry: increasing the light emitting area

much larger light emitting area per footprint

reduced cost per photon

down-scaling of wafer cost, processing cost, packaging

cost etc. etc.

only if everything works out OK (growth, IQE, outcoupling, processing)


A “quasi GaN substrate”: superior properties of 3D semiconductor material

• high aspect ratio / small footprint • high crystallinity / “zero defects” • fast growth rate: 50 µm/h • high surface-to-volume ratio, large increase of active area • vertical architecture possible • „multi-dimensional“ platform:

LEDs, sensing, power electronics … • no strain even when grown on mismatched substrates (like

on silicon)

3D GaN (TUBS)


The nanorod approach …

nanorods and nanowires are building blocks for nanoscale electronics

S.F.Li, … AW et al. 2010

substrate

ZnMgO

ZnMgOZnO well

ZnO Ev Ec

dwell

dnanopillardlayer


Selective Area Growth of GaN NanoLEDs

Si3N4 and SiO2 can be used to achieve

good growth selectivity

12 µm


Photolithography : lateral patterning

surfaces must be very flat, when very small structures are to be realised status @ TUBS: > 500 nm possible > 1µm stable


Nanoimprint - Lithography

27

Embossing of a stamp into a polymer Polymerisation by UV irradiation stamp needs to be transparent (better than thermal nanoimprint) flexible polymer stamp (soft-stamp) can deal with non-flat surfaces status @ TUBS: >100 nm


Silicon Wafer with Nanorod Fields

D = 400 nm – 2 µm varying pitch

photolitho or nanoimprint

deep etched silicon soft mask for nanoimprint


Deep etching by plasma chemistry

ICP dry etching (flourine based) for nitrides, oxides and silicon based 3D structures


3D GaN vertical architecture Homogenous growth of Ga-polar GaN columns

Ga-polar GaN columns on patterned

SiOx/GaN/sapphire


3D GaN vertical architecture Alternative combined top-down approach

Alternative combined top-down approach ICP dry etching and wet chemical etching

Results relatively smooth a-plane sidewalls, easy reproducible adjustment of NW diameter, more defined doping control

I. Film growth II. Cr mask

III. ICP dry etching (SF6, H2)

IV. Wet etching (KOH)

GaN

Sapphire

Cr

For channel


3D GaN vertical architecture Nanowire size optimization

Wet etching optimization temperature, etch time, etch solution

Etch rate 62 – 82 nm/h Very high aspect ratio up to > 60 Small size diameter < 50 nm

1 h

20 min

2 h

4 h 6 h

ICP

90°C


How to analyse GaN based microrods ?


FE-SEM Tescan Mira3 GMH

Improved spatial resolution for characterization by BSE, EBIC, CL and EL (via Manipulators) Nondestructive electro-optical investigation of 3D structures on whole wafers

Simultaneous detection of up to four signals (dedicated ADCs) for imaging. Special parabolic mirror with a notch for investigation of wafers up to 4“ at tilt ≤ 30°.

Detectors: ET-SE, In-Beam SE, low-kV BSE, EBAC/EBIC, beam rocking, probe ≤ 200 n

Gatan MonoCL4 with custom designed mirror

[J. Ledig et al., “Nondestructive inspection of 4’' wafers in bird's eye view by an FE-SEM” imaging & microscopy, vol. 18, no. 2, 2016.]


Contacting inside an ensemble of core-shell LEDs electro-optical characterization

SE and EBIC image visualizing the light emitting region of the center structure contacted by a tungsten probe tip. CL excitation mapping and spectra from excitation along the sidewall.

[J. Ledig et al., “Nondestructive inspection of 4’' wafers in bird's eye view by an FE-SEM” imaging & microscopy, vol. 18, no. 2, 2016.]


STEM/CL of GaN:Si microrod: influence of defects on quantum well

High Low

CL: M.Müller, F.Bertram, J.Christen

Optimisation of shell growth: PL-IQE ~ 60%


Processing of Core-Shell GaN blue-emitting microrod LEDs

Schimpke, AW, Lugauer, Strassburg, et al, phys.stat.sol.A(2016) 201532904


38

38 38

Towards Nanorod and Microrod LEDs Processes for 3D LED Chip Fabrication

• AlOx and BCB deposition • BCB etch • AlOx etch • ITO deposition (p-contact) and

metal contact preparation • Mesa definition (exposure of n-GaN

cores for n-contact) • Pad metallization

440 nm

3D & Core-shell

M. Strassburg, M. Mandl, T. Schimpke, T. Hero, D. Scholz, C. Kölper, M.Sabathil OSRAM Opto Semiconductors GmbH


White light generation by phosphor conversion using close coupled phosphor

GaN

Active Area

Phosphor

Blue microrod LED chips

• Improved light extraction from LED die and thermal control of converter • Significant reduction of grain size compared to conventional converter material without

reduction in efficiency is required • Deposition of µ-grain phosphor between high-aspect ratio microrods

Standard phosphor

4 µm

2 µm

10.000 x


EU-FP7


White emission from 3D-LEDs by conversion

p-contact metal

transparent conductive oxide

isolation layer

micro grained converter

• Chip-processing Process steps adopted to the array Blue emission from processed 3D-LEDs

n-doped GaN-contact layer sapphire substrat

3D-L

ED

n-contact metal

White emitting LED 3D-geometry enables new concepts:

micro grained converter inside the gaps of the 3D-LED column array forward scattering improved cooling of the converter

First demonstration of a converted white emission based on core-shell LEDs

Leuchtstoff



Towards Nanorod and Microrod LEDs Bright emission from Core-shell microrod LED

I = 5mA

41

Full-4inch wafer processing


Laser-Lift-Off: removal of GaN LED thin film from the saphire substrate

An Excimer-Laser destroys the interface between GaN and saphire substrate. GaN LED can then be transferd to another carrier (e.g. a glass or silicon carrier)


Summary: nanoLEDs for solid state lighting

• 3D approach could be of more general importance to GaN technology

• Core-shell LEDs are a smart way to go beyond scaling laws of conventional planar technology.

Gan FIN technology could be interesting: LEDs, vertical electronics, sensing

funded by the european union - ga 737089 kick-off … by the european union - ga 737089 kick-off...

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