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Characteristic of InGaN/GaN Laser Diode Grown by a Multi-Wafer MOCVD

System

Y. Park, B.j. Kim, J. W. Lee, O. H. Nam, C. Sone, H. Park, Oh Eunsoon, H. Shin, S. Chae, J. Cho, Ig-Hyeon Kim, J.S. Khim, S.

Cho and T.I. Kim

MRS Internet Journal of Nitride Semiconductor Research / Volume 4 / Issue 01 / January 1999

DOI: 10.1557/S1092578300000570, Published online: 13 June 2014

Link to this article: http://journals.cambridge.org/abstract_S1092578300000570

How to cite this article:

Y. Park, B.j. Kim, J. W. Lee, O. H. Nam, C. Sone, H. Park, Oh Eunsoon, H. Shin, S. Chae, J. Cho, Ig-Hyeon Kim, J.S. Khim, S.

Cho and T.I. Kim (1999). Characteristic of InGaN/GaN Laser Diode Grown by a Multi-Wafer MOCVD System . MRS Internet

Journal of Nitride Semiconductor Research, 4, pp e1 doi:10.1557/S1092578300000570

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MRS Internet J. Nitride Semicond. Res. 4, 1 (1999). 1

Internet Journal ResearchNitride Semiconductor

Characteristic of InGaN/GaN Laser Diode Grown by a

Multi-Wafer MOCVD System

Y. Park

, B. J. Kim

, J. W. Lee

, O. H. Nam

, C. Sone

, H. Park

, Eunsoon Oh

, H. Shin

, S. Chae

J. Cho

, Ig-Hyeon Kim

, J.S. Khim

, S. Cho

and T.I. Kim

Samsung Advanced Institute of Technology,

(Received Wednesday, January 6, 1999; accepted Tuesday, January 19, 1999)

InGaN/GaN multi-quantum well (MQW) laser diodes (LDs) were grown on c-plane sapphire

substrates using a multi-wafer MOCVD system. The threshold current for pulsed lasing was 1.6 A

for a gain-guided laser diode with a stripe of 10 x 800

. The threshold current density was 20.3

kA cm

-2

and the threshold voltage was 16.5 V. The optical power ratio of transverse electric mode

to transverse magnetic mode was found to be greater than 50. The characteristic temperature

measured from the plot of threshold current versus measurement temperature was between 130 and

150K.

1 Introduction

Nitride semiconductor short wavelength laser diodes

(LD) have attracted much attention as a light source for

the optical data storage. Since Nichia Co. reported

pulsed lasing in an InGaN multi-quantum well (MQW)

LD in the end of 1995, [1] signiﬁcant progress has been

made in the development of blue LD’s. Nakamura et al.

has already demonstrated a blue LD with lifetime in

excess of 10,000 hrs. [2] Although Nichia’s conspicu-

ous successes have stimulated the nitride research soci-

ety during the last three years, until recently a limited

number of research groups in the United States and

Japan reported continuous wave [3] [4] [5] or pulsed

lasing. [6] [7] [8] [9] In this paper, we report InGaN/

GaN MQW LD operated under pulsed conditions.

2 Experiment

The LD structure shown in Figure 1 was grown on a c-

plane sapphire substrate using a multi-wafer MOCVD

system into which three 2” wafers can be loaded in a

time. To our knowledge, this is the ﬁrst report on

InGaN/GaN MQW LD grown by a mass production

scale MOCVD reactor in the open literature. TMGa,

TMIn, TMAl, Cp

Mg, NH

, and SiH

were used as

material sources for the structure growth. The reactor

pressure was maintained at 100 torr during the growth.

In order to form gain guided LD’s the structure was

etched using chemically assisted ion beam etching

(CAIBE) until the n-type GaN layer was exposed. A Pd/

Au contact was formed onto the p-type GaN, and a Ti/Al

contact onto the n-GaN. The laser facets were formed

by CAIBE. No mirror coating was employed on the

facet surface. Fabricated LDs were measured under

pulsed current conditions with pulse widths ranging

from 100 ns to 1

sec at 1 kHz.

3 Results

Figure 2, Figure 3, Figure 4, Figure 5 show typical fea-

tures proving that the diodes lased. Figure 2 shows L-I-

V characteristics of one of the LDs with a stripe of 10

m x 800

m. The lowest threshold current was found

to be 1.6 A, corresponding to a threshold current density

of 20.3 kA cm

-2

. The threshold voltage of the device at

the threshold current was 16.5 V. Figure 3 shows the

polarized light output intensity as a function of current

for another LD, whic hwas measured under a pulse con-

dition of 200 ns width at 1 kHz. It is clear that the

emission was strongly polarized in transverse electric

(TE) mode above the threshold current of 1.9 A, which

is a good indication of lasing operation. The ratio of TE

to transverse magnetic (TM) mode was found to be

larger than 50. Figure 4 shows optical spectra of one of

the LD’s. The spectra were collected using a monochro-

mator and a photon multiplier with a resolution of 0.1 A.

Above the threshold current, strong and well-deﬁned

mode spectra were observed. They have several groups

of sub-band emissions in the wavelength range of 415 to

421 nm with a peak spacing of around 0.72 nm. Figure

2 MRS Internet J. Nitride Semicond. Res. 4, 1 (1999).

5 illustrates a narrow far-ﬁeld pattern of the stimulated

emission.

The sub-band emissions in the spectra shown in Fig-

ure 4 are known to be composed of many longitudinal

modes. [5] [10] Figure 6 is a spectrum obtained at a

higher resolution on the LD wit ha stripe of 10

m x 800

m. The sample was measured with a pulse width of 1

sec at 1 kHz. It is observed that each sub-band consists

of several sharp peaks with a separation of 0.043 nm.

Assuming that these peaks arises from the longitudinal

modes of the LD, the mode separation

∆λ

is given by

∆λ

/ 2Ln

where n is the effective refractive index,

is the

emission wavelength, and L is the cavity length. Given

the values, 0.043 nm, 416.6 nm , and 800

m for

∆λ

and L, respectively, we obtained 2.52 as the refractive

index n. This value is close to a value calculated from

the optical modes of the structure and similar to a value

Nakamura et al. used in their early work on the pulsed

lasing. [11] However, somewhat larger effective refrac-

tive indexes of 3.3 and 3.6 have been reported in other

papers. [5] [10]

Figure 7a shows L-I characteristics of one of the

LD’s with a stripe of 10

m x 1200

m at different tem-

peratures ranging from 0 to 100

C. The pulse width

was 200 ns at 1 kHz. As shown in Figure 7a, the LD

lased up to a temperature as high as 100

C. However,

the LD showed a degradation phenomenon at 100

C. It

failed at greater current than 5 A. It is certain that with

increasing measurement temperature threshold current

increases. The temperature dependence of threshold

current is shown in Figure 7b. The calculated character-

istic temperature was 155K for around room tempera-

ture operation and 133K for higher temperature

operation. These values are comparable to those of other

group’s InGaN LDs. [5] [10] [12] Kuramata et al. has

reported a similar change in the characteristic tempera-

ture. [5] It is worth noting that the LD showed a kink in

the L-I plot at temperatures higher than 60

C with more

apparent appearance at higher temperature. Nakamura et

al. suggested that such a kink in the L-I plot for their

high power LD was due to the change in emission mode.

[13] More work is necessary to verify the origin of the

kink.

4 Conclusion

We demonstrated the room temperature pulsed lasing of

InGaN/GaN MQW blue LD grown by a multi-wafer

MOCVD system. Threshold current density was found

to be 20.3 kA cm

-2

for 10

m x 800

m stripe LD. The

operating voltage at this threshold current density was

16.5 V. Above the threshold current a strong and well-

deﬁned emission mode with a peak spacing of 0.72 nm

was observed. The refractive index calculated from the

spacing between longitudinal modes was 2.52. The

measured characteristic temperature was between 130

and 150K.

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MRS Internet J. Nitride Semicond. Res. 4, 1 (1999). 3

FIGURES

Figure 1. A schematic of the fabricated LD

Figure 2. L-I-V characteristic of the LD

Figure 3. Polarized light output intensity of the LD.

Figure 4. Spectra of the pulsed lasing

Figure 5. A far-ﬁeld pattern of pulsed lasing.

4 MRS Internet J. Nitride Semicond. Res. 4, 1 (1999).

Figure 6. Subband emission consisting of sharp longitudinal

modes.

Figure 7a. Temperature dependence of L-I characteristics of the

Figure 7b. Threshold current as a function of measurement

temperature.