425°C生长InAs/GaAs量子点激光器的高性能研究

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"High-performance InAs/GaAs 量子点激光器的研究，重点比较了在425°C和500°C生长的InAs量子点层的性能差异。425°C生长的量子点激光器展现出更好的性能指标，如较低的阈值电流密度和输出功率。" 这篇研究集中在InAs/GaAs量子点激光器的性能优化，通过对比不同生长温度（425°C和500°C）下InAs量子点层对激光器性能的影响。激光器的结构采用脊形波导设计，便于制造和测试。实验结果显示，425°C生长的InAs量子点层的激光器表现出更优的特性。量子点（Quantum Dot, QD）是一种纳米尺度的半导体结构，因其尺寸小于激子波尔半径，因此能级高度量子化，这使得量子点激光器具有许多独特的光学性质，例如更窄的线宽、更高的光增益以及更稳定的运行温度。在这项研究中，作者们使用气体源分子束外延（Gas Source Molecular Beam Epitaxy, GSMBE）技术来生长量子点层。在425°C生长的InAs量子点激光器中，观察到的关键优势包括更低的阈值电流密度。阈值电流密度是衡量激光器启动并维持连续激光发射所需最小电流的参数，较低的阈值电流密度意味着更高效的能量转换和更低的运行功耗。此外，这些激光器还显示出较高的输出功率，这通常与更高的光增益和更好的载流子注入效率有关。更高的输出功率意味着激光器在特定工作条件下能够提供更强的光信号。激光器的性能受到多个因素的影响，包括量子点的尺寸控制、形貌、密度以及材料的质量。生长温度作为关键的工艺参数，影响着量子点的形成、尺寸分布和表面态。在这个研究中，425°C被认为是更为理想的生长条件，可能因为这个温度下InAs量子点的形态和排列更加有序，导致了更好的光学性能。此外，系统性的研究方法对理解量子点激光器性能与生长条件之间的关系至关重要。通过对比不同温度生长的激光器，研究人员可以深入探索量子点的生长动力学，进而优化生长过程，实现更高性能的量子点激光器。这项工作不仅对半导体激光器的设计和制造有直接指导意义，也为未来的量子点技术提供了重要的实验数据，尤其是在高温生长条件下实现高性能激光器的可能性。这将有助于推动量子点技术在光通信、生物医学成像、光电子器件等领域的应用。

COL 11(6), 061401(2013) CHINESE OPTICS LETTERS June 10, 2013

High-performance InAs/GaAs quantum dot laser with dot

layers grown at 425

◦

Li Yue (

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, Qian Gong (

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, Chunfang Cao (

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, Jinyi Yan (

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, Yang Wang (

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Ruohai Cheng (

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, and Shiguo Li (

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Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences,

Shanghai 200050, China

Department of Electronic Communication and Technology, Shenzhen Institute of Information Technology,

Shenzhen 518172, China

∗

Corresponding author: yueli@mail.sim.ac.cn

Received December 29, 2012; accepted March 28, 2013; posted online May 30, 2013

We investigate InAs/GaAs quantum dot (QD) lasers grown by gas source molecular beam epitaxy with

different growth temperatures for InAs dot layers. The same laser structures are grown, but the growth

temperatures of InAs dot layers are set as 425 and 500

◦

C, respectively. Ridge waveguide laser diodes

are fabricated, and the characteristics of the QD lasers are systematically studied. The laser diodes with

QDs grown at 425

◦

C show better performance, such as threshold current density, output power, internal

quantum efficiency, and characteristic temperature, than those with QDs grown at 500

◦

C. This finding

is ascribed to the higher QD density and more uniform size distribution of QDs achieved at 425

◦

OCIS codes: 140.5960, 140.2020, 230.5590, 300.6360.

doi: 10.3788/COL201311.061401.

Self-assembled InAs quantum dots (QDs) as active me-

dia for laser diodes have elicited much attention be c ause

of their atomic-like quantum structures, which result in

unique optical and electrical properties very different

from those of traditional semiconductor lasers, such as

quantum wells a nd bulk material lasers

[1−4]

. To date,

most studies focus on InAs/GaAs system QD lasers; good

laser performances in terms of low threshold current den-

sity, high characteristic temperature, high gain profile,

large modulation bandwidth, and good wavelength sta-

bility have been obtained

[5−11]

. For InAs/GaAs QD

lasers, growth temperature and growth equipment have

impo rtant functions in the density and size uniformity

of QDs, which strongly inﬂuences the performance of

the laser diode. Aside from other growth techniques,

such as metal organic vapor-phase epitaxy, chemical-

beam epitaxy, and solid source molecular-beam epitaxy,

gas source molecular-beam epitaxy (GSMBE) has also

been demonstr ated as a successful growth technique to

obtain high-performance QD lasers

[8,12,13]

. In particular,

the GSMBE technique has the ability to grow InAs QD

on GaAs substrate in a wide range of growth tempera-

ture, thus po sing a great effect on the dot density and

size distribution of QDs. Joyce et al.

[14]

grew InAs QD

on GaAs substrate at temperatures between 350 and 500

◦

C. Smaller QDs formed at 350

◦

C with a high density of

2.6×10

−2

, whereas larger QDs were obta ined at 500

◦

C with a low density of 5×10

−2

. In general, good

performance of InAs/GaAs QD lasers can be achieved

by growing the QD layer at high growth temperatures

of ab out 500

◦

C to obtain high optical quality. Grow-

ing QDs at low temperatures should be avoided for laser

applications. However, we found that doing so may re-

sult in better device performance . In this study, we grew

the same QD laser structure, but the InAs QDs were

grown at 425 and 500

◦

C, respectively. Laser diodes

were fabricated, and laser p e rformances were character-

ized. The QD lasers with QDs grown at a lower temper-

ature of 425

◦

C e xhibit better perfor mance than those

with QDs grown at 500

◦

C. QDs grown at lower temper-

ature have higher dot density and uniform siz e distribu-

tion, which are important for the improvement of device

performance.

The samples were grown on n-ty pe (00 1)-oriented GaAs

substrates by GSMBE. After thermally removing the na-

tive oxide layer from the substrate, a 500-nm-thick Si-

doped GaAs buffer layer was grown, followed by a 1 500-

nm-thick Si-doped Al

0.3

0.7

As cladding layer. The ac-

tive region contained five-stacked InAs QD laye rs sep-

arated by 40-nm-thick GaAs layers. T he active region

was sandwiched by 20 periods of Al

0.3

0.7

As/GaAs

(2 nm/2 nm) s uper lattices as waveguide. Finally, the

structure was finished by gr owing a 1 500-nm-thick Be-

doped Al

0.3

0.7

As cladding layer and a 200-nm-thick

Be-doped GaAs contact layer. To study the effect of QD

layer growth temperature, two wafers were grown with

the same structure mentioned above but with QD layers

grown at 425 and 500

◦

C which were marked as samples

A and B, respe c tively. To achieve desirable gain, the InAs

QD deposition thickness was optimized as 1 .8 monolayers

(ML) for 42 5

◦

C and 2.2 ML for 500

◦

C. Ridge waveg-

uide las e r diodes with strip width of 10 µm and differe nt

cavity lengths were fabricated. All lasers were as-cleaved

without facet coating. The chip was bonded on a copper

heat-sink whose tempe rature can be adjusted from 20 to

◦

C. For photoluminescence (PL) measurements, the

sample was excited by the 514-nm line of an Ar

laser.

Lasing spectra were measured by a Fourier transfo rm in-

frared spectrometer equipped with an InSb detector with

a resolution of 0.125 cm

−1

. The output power was mea-

sured by a Melles Griot optical power meter, including

an integrating Ge detector. All measurements were car-

ried out under continuous wave (CW) mode.

Figure 1 shows the PL spectra measured at 7 7 K for

1671-7694/2013/061401(4) 061401-1

 2013 Chinese Optics Letters

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