Pis’ma v ZhETF, vol. 111, iss. 5, pp. 301 - 302

March 10

Microstructural characterization of V-defects in InGaN/GaN

multiquantum wells

H. Wang⁺¹⁾, G. Jin⁺, Q. Tan^+∗

⁺Academy of Electronic Information and Electrical Engineering, Xiangnan University Chenzhou, 423000, China

^∗Institute of Physics and Information Science, Hunan Normal University, Changsha, 410081, China

Submitted 27 December 2019

Resubmitted 2 February 2020

Accepted 2

February 2020

DOI: 10.31857/S0370274X20050045

GaN-based materials have wide bandgap and good

at 1150^◦C for 2 h with a V/III flux ratio of 1500. Then,

thermal stability, which are widely used in photoelec-

thirteen pairs of InGaN (2.7 nm)/GaN (11.5 nm) MQW

tric and microelectronic devices, such as light-emitting

were grown at 860^◦C. The MQW were capped with

diodes, laser diodes, detectors, high electron mobility

900Å of Al_0.06Ga_0.94N. Cross-section-view transmission

transistors, etc [1, 2]. But, owing to the lattice mismatch

electron microscopy (TEM) samples were prepared by

and thermal mismatch between GaN and substrate in

wedge polishing followed by Ar⁺ ion milling. TEM mea-

heteroepitaxy, there are high density defects in GaN ma-

surements were carried out by a Philips CM200 high-

terials, such as V-defect, dislocation, point defect and

resolution transmission electron microscope at an oper-

so on. In the InGaN multi-quantum well (MQW) struc-

ating voltage of 200 kV.

ture, the so-called V-defects are often observed [3, 4].

Low magnification dark field TEM (Fig. 1) showed a

These defects have a hexagonal inverted pyramidal ap-

number of threading dislocations in the MQW. On the

pearance with {1010} walls, and they are limited by

a hexagon in the basal plane [4]. The V-defects often

nucleate on threading dislocations (TDs), and crossed

with the MQW just above the underlying layer. Several

suggestions, such as strain release, low surface mobil-

ity of the adatoms on the InGaN layer and/or reduced

Ga incorporation on the {1011} planes in comparison to

the {1000} surface, have been proposed to explain the

generation of this V-defect [5,6]. The model established

by Northrup and Neugebauer [7] using the first princi-

ple calculation shows that indium is a kind of differential

surfactant. The indium reduces surface energy of {1011}

relative to {1000}, which promotes the V-shaped defect

with {1011} opening from the threading dislocation.

Fig. 1. Cross-section dark field TEM images of the

All layers of the samples were grown on a c-sapphire

InGaN/GaN MQW. The diffraction spot was marked in

(0001) substrate by MOVCD. During the MOCVD

upper right corner

growth, trimethylgallium, trimethylindium and ammo-

nia were used as precursors of gallium, indium and nitro-

left side of the image we can see a threading dislocation

gen. Biscyclopentadienyl magnesium and disilane were

reaching the MQW, and it does not go out from the top

used as p- and n-type dopant sources, respectively. After

of the defect, instead of stopping at the quantum well.

thermal cleaning of the substrates in hydrogen environ-

Nevertheless, on the right side of the image, a threading

ment at 1100^◦C for 10 min, a 25 nm thick GaN nucle-

dislocation enters the GaN overlay from the last quan-

ation layer was deposited at 550^◦C. Subsequently, an

tum well. In the micrograph a mixed-type threading dis-

undoped GaN (u-GaN) layer and a n-type doped GaN

location (labeled with M) and a pure-edge TD (labeled

(n-GaN) layer were grown on the low-temperature GaN

with E) can be seen. The mixed-type threading disloca-

tion was decomposed into an a-type and a c-type dislo-

¹⁾e-mail: whycs@163.com

cation. The a-type component dislocation bends to an

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2020

301

302

H. Wang, G. Jin, Q. Tan

interface direction contributing to a misfit dislocation in

play a central role in the nucleation of V-defects, the

the InGaN/GaN interface, afterwards from an interface

strain (and comparable strain energy) in InGaN MWQ

to another threading dislocation. Due to the g · b = 0

on the pyramid planes should be the same as that on

invisibility criterion, the c-type component dislocation

the (0001) plane (the mismatch of GaN and InN in a-

is not seen, because this decomposition reaction is an

and c-directions is about 12 %). Therefore, strain relief

energetically neutral reaction [8]. This dislocation has a

should not be the reason for the growth of V-defects. On

Burgers vector b = 1/3〈1120〉 in the {0001} sliding sur-

the contrary, the decrease of GaN incorporation (and

face, which alleviates the mismatch in this region. Due

growth rate) in the pyramid plane compared with the

to the poor compatibility between GaN and InN, In-

(0001) plane is the main reason for the growth of V-

rich clusters have been found in InGaN quantum wells,

defects. The direction of the inclined plane terminating

which are caused by the fluctuation of indium compo-

quantum well is determined by the relative growth rate

sition [9]. The fluctuation of the In components in the

of the material in the V-defect compared to the growth

quantum well may cause the decomposition reaction of

in the adjacent (0001) plane. In the normal growth of

the threading dislocation, which results in the mismatch

InGaN/GaN MQW, the growth temperature of GaN

strain-induced dislocation. The threading dislocations

barrier is about 290^◦C lower than that of high tem-

associated with this defect have different characteristics.

perature GaN to restrain the re-evaporation of In. Un-

When the dislocations have c-component, the possibility

der the condition of nominally used for MQW growth,

of nucleation increases.

the more refractory component (GaN in this case) has

In Figure 2, the 13-pair MQW cross-sectional TEM

limited surface diffusion, so the defect morphology is

micrograph shows that the V-defects include some dis-

controlled by dynamics. At high temperature, when the

surface diffusion rate is high, the V-defects are flattened

rapidly by GaN.

Full text of the paper is published in JETP Letters

journal. DOI: 10.1134/S0021364020050021

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