光電半導體元件與高功率雷射系統之研究

光電半導體元件與光電半導體元件與高功率雷射系統之研究高功率雷射系統之研究

陳秀芬

楊勝州

屠嫚琳

吳佩璇

謝尚衛

2003/6/6 光電半導體專題研究(91學年度) 2

Outline Outline Experimental and numerical investigation of 590-nm

AlGaInP light emitting diodes and vertical-cavity surface-emitting lasers ( 陳秀芬 )

紫光氮化銦鎵面射型半導體雷射之設計與分析 ( 楊勝州 )

Numerical study on the optical properties of a 655-nm vertical-cavity surface-emitting laser for PMMA-d8 optical fiber communication ( 屠嫚琳 )

Investigation of the characteristics of electronic overflow in 415-nm violet InGaN semiconductor laser ( 吳佩璇 )

Introduction of passive Q-switching theory and tunable Cr:YSO Q-switched Cr:LiSAF laser ( 謝尚衛 )

Experimental and numerical investigation of 590-nm AlGaInP

light emitting diodes and

vertical-cavity surface-emitting lasers

指導教授：郭艷光博士報告者：陳秀芬

班級 :物理系四年乙班


Abstract We experimentally investigated the optical

properties of several 590-nm AlGaInP light emitting diodes of different structures with a photoluminescence measurement system.

The optical properties of the 590-nm AlGaInP multiple quantum well structures are also numerically investigated with the PICS3D simulation program.

In the mean time, the optical characteristics of the 590-nm AlGaInP vertical-cavity surface-emitting lasers are numerically evaluated with the PICS3D simulation program.


PL spectrum of 590-nm LEDs at room temperature

The intensity of Sample A is much lower than that of Sample B. Both of their wavelength is about 590 nm. The efficiency of Sample C is worse, and its wavelength is about 605 nm.

0

200

400

600

800

1000

520 540 560 580 600 620 640 660

Sample ASample BSample C

Wavelength (nm)

Inte

nsit

y (a

.u.)


PL spectrum of Sample B at different temperatures

It’s obvious that the central wavelength has “blue shift” when the temperature decreases. In the mean time, the intensity becomes higher, and FWHM (full width at half maximum) becomes smaller.

0

1000

2000

3000

4000

540 560 580 600 620

160 K240 K320 K

Wavelength (nm)

Inte

nsit

y (a

.u.)


Wavelength and intensity of Sample B as a function of temperature

When temperature decreases, the central wavelength becomes shorter and the intensity becomes higher.

570

575

580

585

590

595

600

1000

2000

3000

4000

5000

150 200 250 300 350

Wav

elen

gth

(nm

)

Inte

nsit

y (a

.u.)

Temperature (K)


Wavelength and intensity of Sample B as a function of input power

If we increase the input power at room temperature, the central wavelength does not change obviously but the intensity increases accordingly.

580

585

590

595

600

605

610

1000

1500

2000

2500

3000

3500

30 40 50 60 70 80

Input Power (mW)

Inte

nsit

y (a

.u.)

Wav

elen

gth

(nm

)W

avel

engt

h (n

m)


Comparison between experiment and simulation

We used the PICS3D program to simulate the 590-nm active region. The results obtained from simulation are in good agreement with those obtained experimentally.

570

575

580

585

590

595

600

150 200 250 300 350

ExperimentSimulation

Wav

elen

gth

(nm

)

Temperature (K)


Initial structure of 590-nm VCSEL

The material of active region is

Al0.095Ga0.46In0.445P (5 nm) / Al0.25Ga0.25In0.5P (10 nm) ,

which has a strain of about 0.27 ％ .


L-I curves of different well materials

The Al0.13Ga0.37In0.5P (5 nm) / Al0.25Ga0.25In0.5P (10 nm) is used as the material of the unstrained active region of the 590-nm VCSEL. The VCSEL with strained active region has lower threshold current and better laser efficiency.

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4

In=0.445In=0.5

Current (mA)

Las

er P

ower

(m

W)

紫光氮化銦鎵面射型半導體雷射之設計與分析

指導教授：郭艷光博士報告者：楊勝州

班級 :物理系四年甲班


Introduction

用一套由加拿大 Crosslight 公司所提供的商用套裝模擬軟體叫 PICS3D 模擬軟體來做模擬。

由於氮化物剛在發展階段，其特性不是很明確，所以我就設計一個由電激發出紫光的氮化銦鎵面射型半導體雷射來探討它的發光特性及雷射輸出效能。

參考文章把發光波長設計在 408 nm 。


初始元件結構圖

活性層量子井材料在井 (well) 部分為 3 nm 的 In0.087Ga0.913N ，井障 (barrier)為 4 nm 的 In0.001Ga0.999N ， spacer 厚度為 0.15 m 的 GaN ， DBR 的材料成分設計為 GaN 與 Al0.27Ga0.73N ， n-type 的 DBR 對數為 60 對，其反射率為99.6 ％， p-type 的 DBR 對數為 50 對，摻雜濃度同樣為 1x1018 cm-3 ，每隔20 對 DBR 增加一層氮化鎵薄膜為緩衝層以緩衝應力，最後把整個元件半徑設計為 10 m 。


發光功率與電流關係圖

0

1

2

3

4

5

5 10 15 20

Out

put P

ower

(m

W)

Current (mA)

當元件結構設計為兩個量子井且共振腔長度為一個波長時其雷射光輸出的臨界電流約為 15.5 mA 左右。


不同 n-DBR 對數的反射率頻譜圖

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

40 pairs50 pairs60 pairs

390 395 400 405 410 415 420 425 430

Re

flect

ivity

of

n-D

BR

Wavelength (nm)

由上圖中可看出當我們把 n-DBR 對數設計為 50 對時，其雷射波長(408 nm) 的最大反射率為 98.8 ％，若增加到 60 對時其反射率增加到99.6 ％，且隨著 DBR 對數的增加，反射率所含蓋的頻譜範圍小。


溫度與發光波長關係圖

由圖中可得知：當溫度為 20 K 時，其發光波長約在 397.8 nm 左右，也就是說隨著溫度的降低，整個元件的發光波長會往短波長移動，會有藍位移的現象發生。

396

398

400

402

404

406

408

410

0 50 100 150 200 250 300 350

Wa

vele

ng

th (

nm

)

Temperature (K)


不同元件半徑下的雷射光輸出功率圖

0

1

2

3

4

5

0 3 6 9 12 15 18

06 m08 m10 m

Out

put

Pow

er (

mW

)

Current (mA)

當元件半徑設計為 6 m 時，有最低的臨界電流約 4 mA ，隨著元件半徑的增加，臨界電流也跟著增加，且發光效率變差。

Numerical study on the optical properties of a 655-nm vertical-cavity surface-emitting laser for

PMMA-d8 optical fiber communication

指導教授：郭艷光博士報告者 :屠嫚琳

班級 :工教系四年乙班


Introduction

In this research, I used commercial simulation software PICS3D of Canada Crosslight incorporation.

It can be used to design device structure and material content of 655-nm vertical-cavity surface-emitting laser (VCSEL), so we can obtain all kinds of optic and electronic characteristics.


The absorption spectrum of PMMA-d8

(polymethylmethacrylate-d8) plastic optical fiber

Between 655 and 700 nm, there is a relatively low-loss window, which is about 18 dB/km.


One column and current spreading structures

One column structure of 655-nm red VCSEL

Current spreading structure of 655-nm red VCSEL


L-I curves of one-column structure

The threshold current is about 13.9 mA when radius = 10 m, and 3.5 mA when radius = 5 m.

The simulation results indicate that the VCSEL of a smaller radius has a lower threshold current.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20

r = 5r =10

Out

put P

ower

(m

W)

Current (mA)


Comparison between one column and current spreading structure

The threshold current is about 3.5 mA for one column structure, and 1.6 mA for current spreading structure.The simulation results indicate that the current spreading structure has a better laser performance than that of the one column structure.

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6

one-columncurrent spreading

Out

put P

ower

(m

W)

Current (mA)


Main-side mode suppression ratio (dB)

-10

0

10

20

30

40

50

60

600 620 640 660 680 700 720

Inte

nsity

(dB)

Wavelength (nm)

When the operation current is 0.8 mA (below the threshold current), the main-side mode suppression ratio is about 11 dB. When the operation current is increased to 2 mA (above the threshold current), the main-side mode suppression ratio is increased to about 39 dB.

-5

0

5

10

15

20

25

30

600 620 640 660 680 700 720

Inte

nsity

(dB

)

Wavelength (nm)


Laser performance as a function of temperature

0.0

1.0

2.0

3.0

4.0

5.0

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

300K

310K

320K330K

340K

Out

put P

ower

(m

W)

Current (mA)

Simulation results show that when the temperature is increased, the laser performance deteriorates accordingly.


Characteristic temperature of the VCSEL

1.0

1.5

2.0

2.5

290 300 310 320 330 340 350

Ith

= 0.13491 e ( T / 137. 0652 ) , R= 0.99604 T

hres

hold

Cur

rent

(m

A)

Temperature (K)

Generally, for a semiconductor laser the relation between threshold current and temperature can be characterized by I = I0e

(T/To) mA. The semiconductor laser is

less sensitive to temperature when the characteristic temperature, T0, is high. If we best-fit the data shown in the above figure with this equation, a characteristic temperature of about 137K is obtained.

Investigation of the characteristics of electronic overflow in 415-nm violet

InGaN semiconductor laser

Adviser: Yen-Kuang Kuo

Reporter: Pei-hsuan Wu

Class: Physics 4B


Introduction

The InGaN semiconductor materials have played an important role in the short wavelength laser diodes (LD) and light emitting diodes (LED) owing to the relatively wide bandgap (1.95 ~ 6.2 eV) and high emission efficiency.

The reasons why nitride-based semiconductor lasers have high threshold currents include:

(1) the high density of crystal defects caused by the lack of a lattice-matched substrate, (2) the high resistance of p-type layers.


Initial numerical structure of InGaN DQW laser

The active region is assumed to be 20 m in width and 600 m in length. The reflectivities of the two end mirrors are assumed to be 80% and 90% respectively.

Cap ： GaN (0.1 m, p doping=51017 cm-3)

Cladding ： GaN (0.02 m, p doping=51017 cm-3)

Barrier ： In0.04Ga0.96N

Well ： In0.105Ga0.895N


Well ： In0.105Ga0.895N


Cladding ： GaN (0.25 m, n doping=11018 cm-

3)Buffer ： GaN (0.4 m, n doping=11018 cm-3)

p-contact

n-contact


Issues of investigation

Improve the laser output efficiency (1) Change the number of QW

Improve the electronic overflow (1) Use the blocking layer (AlGaN)

(2) Change the aluminum composition

(3) Increase the p-doping level


L-I curves of the InGaN laser structures ofdifferent quantum well numbers

The threshold current decreases and slope efficiency increases when the number of quantum wells increases.

0

10

20

30

40

50

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300 400 500 600 700 800 900 1000

Single QWDouble QWs

Triple QWs

Out

put L

aser

Pow

er (m

W)

Current (mA)

Las

er P

ower

(m

W)


L-I curves with different p-AlxGa1-xN blocking layers in the InGaN laser structure

When the aluminum composition in the AlxGa1-xN blocking layer, x, increases the threshold currents decreases and the laser performance increases accordingly.

0

50

100

150

200

250

300

0 125 250 375 500 625 750 875 1000

Al=0.05Al=0.15Al=0

Lase

r Pow

er (m

W)

Current (mA)


Using the blocking layer to improve the electronic overflow

Overflow current density and active-layer current density as a function of total current density for (a) initial structure, and (b) improved structure with a blocking layer.

(a) (b)


Increasing the p-doping level to improve the overflow current

The overflow current is reduced with increased p-doping level. We also notice that the laser performance is improved (i.e., the threshold current is lower and the slope efficiency is higher) with increased p-doping level.

P-doping:5× 1017cm-3





Conclusion We use the Lastip numerical simulation to

investigate the current overflow of InGaN DQW structure. The simulation results indicate that it is possible to improve the electronic current overflow by increasing the doping level of the p-type epi-layers and adding an AlGaN blocking layer in the p-type region.

Simulation results suggest that the improved laser structure has a lower threshold current and a higher slope efficiency.

Introduction of passive Q-switching theory and tunable Cr:YSO Q-switched

Cr:LiSAF laser

指導教授：郭艷光博士報告者 :謝尚衛

班級 :物理系四年甲班


Introduction of Cr:LiSAF laser

After the invention of Cr:LiCAF laser in 1988 (tunable from 725 nm to 840 nm and peaked near 780 nm), Steven Payne invented the tunable Cr:LiSAF solid-state laser in 1989.

Cr:LiSAF laser has a long tuning range between 780 and 920 nm and is peaked at 830 nm.

The lifetime of Cr:LiSAF is about 67 s that is much longer than that of Ti:sapphire laser (3.2 s). Hence, Cr:LiSAF laser can be pumped efficiently by flashlamps.


The Cr:YSO Saturable Absorber

Deka et al. made the first spectral analysis of Cr:YSO saturable absorber in 1992.

From many other papers, it has been demonstrated that Cr:YSO is an efficient saturable absorber for ruby, Cr:LiSAF, and Ti:sapphire lasers. Therefore, we expect that we can get high-power laser output from the Cr:LiSAF laser with Cr:YSO saturable absorber.


Definition of quality factor, Q

In an optical resonator the quality factor Q is defined as the ratio of the energy stored in the laser cavity to the energy loss per cycle. Therefore, the quality factor of a laser resonator can be altered by varying the cavity loss.


The three coupled rate equations for Cr:LiSAF

passive Q switching simulation

nNNKNKNKdt

dncaaaaagg ])([ 0

nNKNRdt

dNggggp

g

nNKNNdt

dNaaaaa

a )( 0

In these three equations, n is the photon number in the laser cavity; Ng is the population inversion and Na is the ground state electron numbers of the saturable absorber.


Four- and three-level lasers

Fast

Fast

Level 2Level 3

(Upper Laser Level)

Level 4(Lower Laser Level)

Level 1(Ground State)

Pumping

The dynamics of most lasers, including the Cr:LiSAF laser, can be described by the four energy levels shown above. These lasers are called "4-level lasers" that usually have good laser efficiency.

For some lasers (e.g., ruby) the lower laser level is in fact the ground state. These lasers are called "3-level lasers" that usually have relatively poor laser efficiency.

Emit Light


The structure diagram ofpassive Q switching

Pumping System

Mirror(Total Reflector)

Mirror(Output Coupler)

Active Medium

Laser Output

Saturable Absorber


Output energy and pulsewidth as a function of pumping rate (the wavelength is at 880 nm)

2

2.5

3

3.5

4

4.5

5

30

40

50

60

70

80

0 1 2 3 4 5 6

Out

put E

nerg

y (m

J)

Puls

ewid

th (

ns)

Pumping Rate (1022/sec )

This figure shows that higher output energy and narrower pulsewidth may be obtained at higher pumping level.


Output energy and pulsewidth as a function of reflectivity of output coupler

20

25

30

35

40

45

20

40

60

80

100

120

140

0.7 0.75 0.8 0.85 0.9 0.95

Reflectivity of output coupler

Output Energy (mJ) Pulsewidth (ns)

Simulation results indicate that high output energy and narrow pulsewidth may be obtained when the reflectivity of output coupler is low.


Output energy as a function of ground-state electron number of saturable absorber

From the figure we note that the output energy increases when the ground-state electron number of saturable absorber increases, and when the wavelength of the laser decreases.

Na0(1015

)

4

4.5

5

5.5

6

6.5

7

0 2 4 6 8 10 12 14 16

830 nm 845 nm 860 nm 880 nm

Out

put

Ene

rgy

(mJ)


Conclusion In conclusion, we have experimentally and numerically

investigated the optical properties of 590-nm AlGaInP LEDs and vertical-cavity surface-emitting lasers (VCSELs).

We have designed a VCSEL that has good laser performance in violet spectral region.

We have designed a 655-nm VCSEL for PMMA-d8 optical fiber communication.

We have designed a violet InGaN edge-emitting laser diode for application in optical data storage system.

We have numerically investigated the passive Q-switching performance of a tunable Cr:YSO Q-switched Cr:LiSAF laser.

All of the above research results have been published in the Taiwan optoelectronic and physical annual meetings, and the special issue in 2003 optical fiber communication of the Journal of Optical Engineering (Taipei).

Thank you for your attention!

光電半導體元件與 高功率雷射系統之研究

Documents

光電半導體元件與高功率雷射系統之研究