AlN/AlGaN超晶格提升a面GaN晶体生长质量

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本文研究了通过低压力金属有机气相沉积（MOCVD）技术在r面（11′0 2）蓝宝石衬底上生长非极性a面（112¯0）GaN薄膜。作者们关注的核心问题是AlN / AlGaN超晶格（SLs）对a面GaN晶体质量的提升作用。他们利用X射线衍射（XRD）和原子力显微镜（AFM）等先进的表征手段，对这种新型的生长策略进行了深入探究。实验结果显示，AlN / AlGaN SLs 的引入显著改善了a面GaN的晶体质量。具体表现为表面粗糙度显著降低，以往存在的表面三角凹痕得到了完全消除。这表明超晶格结构能够作为一种有效的质量控制手段，通过调控生长过程中的界面特性，优化材料的生长模式，从而提高晶体的完整性与均匀性。 MOCVD作为一种广泛应用于氮化物半导体生长的技术，其关键在于精确控制化学反应条件和生长参数，以便获得高质量的单晶层。通过将AlN与AlGaN交替沉积，形成周期性的超晶格结构，可以在保持非极性a面GaN的优点的同时，减少生长过程中的缺陷密度，如位错、空位和界面态等，这些因素通常会影响器件性能。此外，XRD的运用不仅确认了材料的晶体结构，还提供了关于晶体生长方向和缺陷结构的信息，有助于评估超晶格对晶体生长导向的影响。AFM则提供了微观尺度上的表面形貌信息，直接揭示了晶体表面粗糙度的改善情况。这项研究对于优化宽禁带半导体材料，如GaN，特别是在高亮度发光二极管（LED）、高压微波器件等领域具有重要意义。通过调控AlN / AlGaN SLs 的设计和生长参数，可以有望实现更高的器件性能和更长的使用寿命，推动相关技术的发展。该论文为理解AlN / AlGaN超晶格在非极性a面GaN生长中的作用机制，以及如何通过优化超晶格结构来提高晶体质量提供了宝贵的实验数据和理论依据，对于进一步改进氮化物半导体的制备工艺具有重要的学术价值和实际应用价值。

Improvements in a-plane GaN crystal quality by AlN/AlGaN

superlattices layers

S.R. Xu



, Y. Hao, J.C. Zhang, X.W. Zhou, L.A. Yang, J.F. Zhang, H.T. Duan, Z.M. Li, M. Wei, S.G. Hu,

Y.R. Cao, Q.W. Zhu, Z.H. Xu, W.P. Gu

Key Laboratory of Fundamental Science for National on Wide Band-Gap Semiconductor Technology School of Microelectronics, Xidian University, Xi’an 710071, China

article info

Article history:

Received 19 December 2008

Received in revised form

2 April 2009

Accepted 26 May 2009

Communicated by R.M. Biefeld

Available online 6 June 2009

PACS:

81.15.Kk

78.55.Cr

Keywords:

A1. Crystal morphology

A3. Metal-organic chemical vapor

deposition

B1. Nitrides

B1. Semiconducting III–V materials

abstract

Non-polar (11 2

0) a-plane GaN ﬁlms have been grown by low-pressure metal-organic vapor deposition

on r-plane (11

0 2) sapphire substrate. We report on an approach of using AlN/AlGaN superlattices (SLs)

for crystal quality improvement of a-plane GaN on r-plane sapphire. Using X-ray diffraction and atomic

force microscopy measurements, we show that the insertion of AlN/AlGaN SLs improves crystal quality,

reduces surface roughness effectively and elimina tes triangular pits on the surface completely.

1. Introduction

GaN-based semiconductors and their heterostructures have

recently attracted considerable interests due to their potential for

visible or ultraviolet light-emitting diodes (LEDs), laser diodes

(LDs) and high-power transistors grown on either c-plane

sapphire or SiC [1,2]. The spontaneous and piezoelectric polariza-

tion ﬁelds present in nitride heterostructures, while typically

being advantageous in electronic devices such as nitride-based

ﬁeld effect transistors, and the strong electric ﬁeld produced by

spontaneous and strain-induced piezoelectric polarizations is in the

c-axis oriented hexagonal GaN [3,4]. These polarization ﬁelds are

undesirable for light-emitting devices whose active regions consist

of quantum wells, because the associated electric ﬁelds separate the

electrons and holes at the opposite interface of the well and reduce

the over lap of their wa v e functions, and then r esults in a reduction of

the recombination efﬁciency in light-emitting devices and a red-

shift of the emission wavelength [5]. To eliminate the internal

polarization ﬁelds, group-III nitride layers have been recently grown

on non-polar planes, such as a- or m-plane. In this case, there are no

polarization ﬁelds perpendicular to the lay er interfaces, because the

polar c-axis lies within the growth plane [6–8]. Howev er, ext ended

defect densities in non-polar (11 2

0) a-plane GaN are very high.

With two-step lateral epitaxial overgrowth (LEO) method, it is

possible to effectivel y reduce the defect densities throughout the

ﬁlm. But the two-step LEO method involves three growth steps and

two processing steps [9,10]. The insertion of AlN/AlGaN superlattices

(SLs) have been used to grow deep ultra violet GaN-based LED

materials on c-plane sapphire, which can eliminate cracking through

strain management and signiﬁcantly decrease threading dislocation

density by acting as an effective dislocation ﬁlt er [11–13].Butthis

method has never been used in the growth of non-polar (11 2

a-plane GaN. Because of the difference in t hermal e xpansion

coefﬁcients between sapphire and GaN, and the different lattice

mismatch along the two main in-plane directions, the strain rev eals

signiﬁcant anisotropic correlation to the growth anisotropic [1 4 ,15].

In the paper, a-plane GaN ﬁlms were grown on r-plane

sapphire with AlN/AlGaN strain-management SLs layers by

metal-organic chemical vapor deposition (MOCVD). Using X-ray

diffraction (XRD) and atomic force microscopy (AFM) measure-

ments, we show that the insertion of AlN/AlGaN SLs effectively

improves crystal quality, reduces surface roughness and elim-

inates triangular pits on the surface.

ARTICLE IN PRESS

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/jcrysgro

Journal of Crystal Growth

doi:10.1016/j.jcrysgro.2009.05.028



Corresponding author.

E-mail address: shengruixidian@126.com (S.R. Xu).

Journal of Crystal Growth 311 (2009) 3622–3625

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