Lasing properties of Arm-Stem type

current injection T-shaped quantum wire lasers

1. Background and Motivation

2.Structure of current injection QWR

3. Lasing properties of QWR

4.Mechanism of current injection

5.Summary

ISSP 　 Univ. of Tokyo 　 M2 　 Makoto Okano

polish,scribereload

GaAs sub.

cleavein situ

as-grown

growth-interruptannealing(600℃)

roughness

atomicallyflat

First growth(600℃)

(001)direction

Cleaved-Edge Overgrowth(500℃)

(110)direction

cleaved surface2.0nm

0.0nm

2um

[001]

[110]

0.Introduction ~about T-shaped QWR

polish,scribereload

GaAs sub.

cleavein situ

as-grown

growth-interruptannealing(600℃)

roughness

atomicallyflat

First growth(600℃)

(001)direction

Cleaved-Edge Overgrowth(500℃)

(110)direction

cleaved surface2.0nm

0.0nm

2um

[001]

[110]

0.Introduction ~about T-shaped QWR

↑Merits ： High uniformity & High controllability of structure.

↓Demerit ： Difficulty of fabrication.

1.Background and Motivation

It is expected that quantum wire laser become better than quantum well laser.

↓Lasing from current injection T-shaped quantum wire (T-wire) had been reported by W.Wegscheider et al. in 1994. 　 However, there has ever been no concrete detail.

↓Recently, we developed growth interrupt annealing technique in 2001. This technique makes T-wire high uniformity possible.

↓We make high uniformity current injection T-wire with the technique, and measure lasing properties of current injection T-wire laser. And then, verify the effects of 1D.

Advantage: Directly estimate carrier density from current.

　　　　　 Easy to measure external quantum efficiency.

2-1.Schemata of two current injection

electron through Arm well

hole through stem well

Arm-Stem type

electron through Arm well

hole through Arm well

Arm-Arm type

15 Number of wires 20

5~110K Operating temp. 30~70K

2.0mA at 100K Threshold current 0.27mA at 30K

0.9% at 100KExternal quantum

efficiency 12% at 30K

2-1.Schemata of two current injection

device propertiesdevice properties

2-2.Structure of Arm-Stem type

Temperature dependenceof Ith and ηout

3. Lasing properties (with HR/HR coating)

14

12

10

8

6

4

2

0

Opt

ical

pow

er[u

W]

3.02.01.00.0Current[mA]

8

7

6

5

4

3

2

1

0

Bia

s-V

olta

ge[

V]

1.0

0.8

0.6

0.4

0.2

0.0 Ext

erna

l Qua

ntum

Effi

cien

cy [

%]

100500

Temperature[K]

7.0

6.0

5.0

4.0

3.0

2.0

Thr

esho

ld C

urre

nt[m

A]

EL

inte

nsity

[arb

.uni

ts]

1.561.551.541.53Photon energy[eV]

I=2.35mAx4x10-2

x3x10-1I=1.50mA

T=100KEL spectra I-V,I-L curve

100K is the best conditions for Ith and ηout. (effect of transport?)

This feature is different than that of Arm-Arm type

I have two questions.

1. Why do Arm-Stem type performs best at 100K?

2. Why is threshold ten times as large as arm-arm type’s?

↓

So, I have measured un-coated sample in region of low current to develop a thorough understanding of these

problems.

4-1. EL spectra with low current (un coated)

EL intensity become strong, but lineshape don’t change.

un-coated

4-2. Absorption/gain spectra with low current

Current increase gradually, but gain spectra don’t change.

Probably, carrier increase imbalance in wire. (Nelectron=Nhole)

un-coatedcf. Optical

pumping 　

Ib = 10uAVb=1.64V

Ib =2.0 ｍ AVb=4.19V

4-3. Bias-Voltage depend. of EL Image

Emission from core layer mainly

hole accumulation hole accumulation and overflow from core.and overflow from core.

Emission from outside of the cladding layer

4-4. Carrier confinement and injection

Hole overflow in arm well because of weak confinement.

Conventional schema

4-4. Carrier confinement and injection

Are hole confined because of high barrier of stem well?

Inversion schema

5.Summary

Future prospects

1. We achieved lasing from Arm-Stem type current injection T-wire lasers. But, device properties are not good. And it performs best at 100K.

Injection efficiency is bad 　　 New schema may make it well.

Strange temperature dependence Effect of carrier transport?

2. When current increase gradually, EL intensity increase and gain spectra don’t change.

We assumed because of hole accumulation and hole overflowing.

1. Measure the uncoated sample, and check the change in gain spectra.

2. Measure the new schema sample, and compared the old schema.

Fin.

Thank you for your 　 kind attention.

See you next time…

20

15

10

5

0

Op

tica

l po

we

r[μW

]

6420

Current[mA]

T=5K

15K

30K

40K

50K

60K

70K80K

14

12

10

8

6

4

2

03.02.82.62.42.22.0

100K

120K

110K

90K

4- ２ .I-L 特性の温度依存性

4- ３ . 温度変化　 (HR コートした試料 )

温度上昇で考えるのは妥当か？ (QCSE 、 BGR ？ )

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

Pe

ak

en

erg

y d

iffe

ren

ce[e

V]

8642

Bias-Voltage[V]

T=120K100K40K5K

97531

各温度で 8～ 10meV程度ピークがレッドシフトする。

↓

温度による BGの変化が表れているとすると

５ K→50K

40K→70K

100K→125K

120K→150K

３ -5. 光励起導波路放出光スペクトル at 5K

励起強度に伴って利得が増加

正孔と電子がバランス→利得発生利得発生

ゆっくりと利得が発生していく。変化し始めるのは 40ｍW以下。利得がブロード。

利得の変化が比較的大きい。変化し始めるのは同じく 40ｍW以下。

明らかに変化し始めるのが遅い。変化し始めるのは 70ｍW。

光励起によって作られたキャリアが、電流によって注入されたキャリアよりも多くなったときに変化が起こるのか？

Waveguide Emission の電圧依存性

バイアス電圧が 2Vの近傍では、下側包絡線のピーク(P1)は上側包絡線のピーク(P2)よりも高エネルギー側にある。

ドープなし試料と同じ傾向

ELが強くなってくるとその影響で、 P1は徐々に P2の低エネルギー側に移動。

過電圧による低エネルギー側の吸収の増加を示唆？？

θee

eE

ll

l

I22

2

sinR4)R1(

R)1(A)(

11

R1

ln1pp

l

min

sum

FSR I

Ip

c

Eln

α ：吸収係数R ：反射率

（ Free Spectral Range ）

Cassidy 法による利得吸収スペクトル導出

Photo Luminescence スペクトル at 5K

IVは非常にきれいで、低温では leakしない。

少し均一性は悪いが、高品質な試料が作製できた。

高電流時 (Ib=2.0mA) の EL-Image

低電流時 (Ib=10uA) の EL-Image

利得吸収スペクトルの電圧依存性1.2～ 1.9Vでの利得の変化は、励起強度依存性に近く、徐々に細線にキャリアが注入されていっていると推測される。

しかし、 1.9～ 3.9Vでは明らかに利得が減少していっているのがわかる。

利得の減少がキャリアの減少によるものであれば、上と下の図はほとんど同じになるはずだが、明らかに異なる。

つまり、利得の減少はキャリアの減少ではなく、なんらかの吸収の増加によるものと考えられる。