WO2014032465A1 - 一种GaN纳米线生长方法 - Google Patents

一种GaN纳米线生长方法 Download PDF

Info

Publication number
WO2014032465A1
WO2014032465A1 PCT/CN2013/077974 CN2013077974W WO2014032465A1 WO 2014032465 A1 WO2014032465 A1 WO 2014032465A1 CN 2013077974 W CN2013077974 W CN 2013077974W WO 2014032465 A1 WO2014032465 A1 WO 2014032465A1
Authority
WO
WIPO (PCT)
Prior art keywords
purity
carrier gas
film
growth
sapphire substrate
Prior art date
Application number
PCT/CN2013/077974
Other languages
English (en)
French (fr)
Inventor
修向前
华雪梅
张士英
林增钦
谢自力
张�荣
韩平
陆海
顾书林
施毅
郑有炓
Original Assignee
南京大学
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 南京大学 filed Critical 南京大学
Publication of WO2014032465A1 publication Critical patent/WO2014032465A1/zh

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
    • C30B25/005—Growth of whiskers or needles
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
    • C30B29/403—AIII-nitrides
    • C30B29/406—Gallium nitride
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape

Definitions

  • the present invention relates to a method of epitaxially growing GaN nanowires by hydride vapor phase.
  • III-V nitride materials (also known as GaN-based materials) mainly composed of GaN, InGaN, and AlGaN alloy materials are new semiconductor materials that have received international attention in recent years.
  • the GaN-based material is a direct bandgap wide bandgap semiconductor material with a continuously variable direct bandgap between 1.9 and 6.2 eV, excellent physical and chemical stability, high saturation electron drift velocity, high breakdown field strength and high thermal conductivity. Excellent performance such as high-frequency, high-frequency, high-frequency High field high power devices, field emission devices, radiation resistant devices, piezoelectric devices, etc.
  • the one-dimensional system of nanomaterials is the smallest dimensional structure that can efficiently transport electrons and optical excitons, and is the most basic structural unit of nanomechanical devices and nanoelectronic devices.
  • the excellent properties of GaN materials as important semiconductor materials make 1D GaN nanostructures have wider potential applications in micro-nanophotonics, photodetector devices, electronic devices, environment and medicine. Therefore, excellent preparation performance and high quality
  • the study of one-dimensional GaN nanostructures and properties has become a frontier topic in current international and domestic research.
  • GaN-based materials there are many methods for growing GaN-based materials, such as metal organic vapor phase epitaxy (MOCVD), high temperature and high pressure composite GaN single crystal, molecular beam epitaxy (MBE), sublimation, and hydride vapor phase epitaxy (HVPE).
  • MOCVD metal organic vapor phase epitaxy
  • MBE molecular beam epitaxy
  • HVPE hydride vapor phase epitaxy
  • the preparation of GaN nanostructures mainly includes anisotropic controllable growth method, VLS (Vapor-Liquid-Solid) and SLS (Solution-Liquid-Solid) mechanism growth method, template-assisted growth method, surfactant method, and nanoparticle self-assembly. And physical or chemical methods such as cutting.
  • the growth of GaN nanostructures can be obtained in a variety of ways, such as MOCVD, MBE, etc., but such equipment is costly and the source material is expensive.
  • the present invention provides a method and process for growing GaN nanowires using a hydride vapor phase epitaxy (HVPE) apparatus using metallic nickel (Ni) as a catalyst.
  • HVPE hydride vapor phase epitaxy
  • the object of the present invention is to provide a method for growing GaN nanowires in a hydride vapor phase epitaxial growth apparatus using metallic nickel as a catalyst. It can produce one-dimensional GaN nanostructure products with excellent performance and high quality.
  • the technical solution of the present invention is a method of preparing GaN nanowires, which uses hydride vapor phase epitaxy (HVPE) equipment to grow GaN nanowires.
  • Metal nickel is used as a catalyst.
  • the metal Ni film is first evaporated; the deposition rate of the Ni film is about 1-2 ⁇ ⁇ / sec, and the thickness of the Ni film is 5 - 50 nm;
  • the sapphire substrate is placed in the HVPE growth system to start low temperature growth of GaN nanowires; growth temperature: 500-85 CTC; high purity N 2 is used as the carrier gas, and the total N 2 carrier gas flow rate is l-5slm ;
  • the Ga source is reacted with conventional high-purity metal gallium and high-purity HC1 to form GaCl, HC flow rate: l-20sccm, and HCl carrier gas flow rate is 10-200sccm.
  • High-purity ammonia gas is used as a nitrogen source, NH 3 flow rate:
  • the growth temperature is especially: 500-650 °C.
  • the HVPE of GaN nanowires is a VLS mechanism. Due to the fast growth rate of HVPE (several hundred micrometers per hour), it is often used to rapidly grow thick films. In the present invention, it is necessary to control growth conditions such that the growth rate of HVPE GaN is lowered to obtain GaN nanowires.
  • the technical solution of the present invention is: depositing metal Ni on a sapphire substrate by physical vapor deposition, and then placing it in an HVPE growth system to grow GaN nanowires at a low temperature.
  • the beneficial effects of the present invention are as follows:
  • the present invention provides a GaN nanowire growth method and process which is simple in process and low in cost. It has a diameter of several tens of nanometers and can reach several micrometers in length.
  • Figure 1 is a photograph of a product of an embodiment of the present invention.
  • the morphology of the GaN nanowires was prepared by changing the NH 3 flow rate with other parameters unchanged (the left, right, and right photographs in Figure 1 correspond to the difference in NH 3 flow rates: 50, 100, and 200 sccm, respectively. : 550, 600 and 650 °C In addition to the nanowire diameter, there is no significant difference in appearance.
  • Figure 2 is a photograph of a product of an embodiment of the present invention. Scanning electron micrograph of GaN nanowires grown by HVPE, in which the insert is a high-magnification photograph.
  • the method and process of the present invention comprises several parts: physical vapor deposition of a metallic Ni film on a sapphire substrate; HVPE low temperature growth of GaN nanowires.
  • the HVPE technology for preparing GaN nanowires includes the following steps:
  • the sample was ultrasonically cleaned in deionized water, ethanol, and deionized water in order to remove residual contaminants on the surface and blow dry with nitrogen.
  • the sapphire substrate is placed in the reaction chamber of the physical vapor deposition apparatus. At a certain reaction chamber pressure and metal source temperature, vapor deposition of the metal Ni film can be started.
  • the Ni film deposition rate is set to be about 1-2 angstroms/second, and the Ni nano film thickness is 5-50 nm. This embodiment selects 20-30 nm.
  • the sapphire substrate coated with the metallic nickel film is placed in the HVPE growth system to start low temperature growth of the GaN nanowires.
  • Growth temperature 550, 600 and 650 °C three temperature conditions; high purity N 2 as carrier gas, total 1 ⁇ 2 carrier gas flow rate l-5slm; high purity metal gallium and high purity HC1 react to form GaCl as gallium source, HC1 Flow rate: l-20 sccm, HCl carrier gas flow rate 10-200 sccm.
  • step 4 After the growth of step 3 is completed, the sample is cooled and the GaN nanowires are obtained. By controlling the parameters in steps 2-4, the metal Ni film can be annealed into ordered particles at the nanowire growth temperature to obtain ordered GaN nanowires.

Abstract

一种制备GaN纳米线的方法，蓝宝石衬底的清洗后，先蒸镀金属Ni薄膜；Ni薄膜厚度5-50nm；将覆有镍薄膜的蓝宝石衬底放入HVPE生长系统中，开始低温生长GaN纳米线；生长温度：500-850℃；高纯N2作为载气，总N2载气流量1-5slm；Ga源采用常规的高纯金属镓和高纯HCl反应生成GaCl，HCl流量：1-20sccm，HCl载气流量10-200sccm；以高纯氨气作为氮源，NH3流量：50-500sccm；生长时间1-10分钟。生长出GaN纳米线。

Description

一种 GaN纳米线生长方法 技术领域
本发明涉及一种用氢化物气相外延生长 GaN纳米线的方法。
背景技术
以 GaN及 InGaN、 AlGaN合金材料为主的 III-V族氮化物材料 (又称 GaN基材料)是 近几年来国际上倍受重视的新型半导体材料。 GaN基材料是直接带隙宽禁带半导体材料， 具有 1.9一 6.2eV之间连续可变的直接带隙， 优异的物理、 化学稳定性， 高饱和电子漂移 速度， 高击穿场强和高热导率等优越性能， 在短波长半导体光电子器件和高频、 高压、 高温微电子器件制备等方面具有重要的应用， 用于制造比如蓝、 紫、 紫外波段发光器件、 探测器件， 高温、 高频、 高场大功率器件， 场发射器件， 抗辐射器件， 压电器件等。
一维体系的纳米材料是可以有效传输电子和光学激子的最小维度结构， 也是纳米机 械器件和纳米电子器件的最基本结构单元。 GaN材料作为重要半导体材料的优良特性使 得一维 GaN纳米结构在微纳光电器件、 光电探测器件、 电子器件、 环境和医学等领域具 有更广泛的的潜在应用前景， 因此， 制备性能优异、 高质量的一维 GaN纳米结构及特性 研究就成为当前国际、 国内研究的前沿课题。
GaN基材料的生长有很多种方法， 如金属有机物气相外延 （MOCVD)、 高温高压合 成体 GaN 单晶、 分子束外延 （MBE)、 升华法以及氢化物气相外延 （HVPE) 等。 GaN 纳米结构的制备主要有各向异性可控生长法、 VLS (Vapor- Liquid-Solid)和 SLS(Solution-Liquid-Solid)机制生长法、 模板辅助生长法、 表面活性剂法、 纳米粒子自组 装及物理或化学方法剪切等。 GaN纳米结构的生长可以采用多种方式如 MOCVD、 MBE 等获得， 但是此类设备价格成本高， 源材料价格高昂。
本发明给出了一种采用金属镍（Ni)做催化剂， 用氢化物气相外延（HVPE)设备生 长 GaN纳米线的方法及工艺。
发明内容
本发明目的是： 提出一种用金属镍作为催化剂， 在氢化物气相外延生长设备中生长 GaN纳米线。 能制备出性能优异、 高质量的一维 GaN纳米结构产品。
本发明的技术方案是， 制备 GaN纳米线的方法， 利用氢化物气相外延 （HVPE) 设 备生长 GaN纳米线。 以金属镍作催化剂， 蓝宝石衬底的清洗后， 先蒸镀金属 Ni薄膜的； Ni薄膜沉积速率设置约为 1-2 ±矣/秒， Ni薄膜厚度 5-50nm; 将覆有金属镍薄膜的蓝宝石 衬底放入 HVPE生长系统中， 开始低温生长 GaN纳米线； 生长温度： 500-85CTC ; 高纯 N2作为载气， 总 N2载气流量 l-5slm; Ga源采用常规的高纯金属镓和高纯 HC1反应生成 GaCl, HC 流量： l-20sccm， HCl载气流量 10-200sccm。 高纯氨气作为氮源， NH3流量： 50-500sccm; 生长时间 1-10分钟。
生长温度尤其是： 500- 650°C。
金属镍作为催化剂时， GaN纳米线的 HVPE为 VLS机制。 由于 HVPE生长速率快 (几百微米 /小时），常用于快速生长厚膜。在本发明中， 需要控制生长条件，使得 HVPE GaN生长速率降低， 以获得 GaN纳米线。 本发明的技术方案为： 用物理气相沉积的方法 在蓝宝石衬底上蒸镀金属 Ni， 然后放入 HVPE生长系统中， 低温生长 GaN纳米线。
本发明有益效果是： 本发明给出了一种工艺简单、 成本低廉的 GaN纳米线生长方法 和工艺。 直径达到数十纳米， 且长度可以达到数微米。
附图说明
图 1 为本发明实施例的产物照片。 在其它参数不变的情况下， NH3流量变化制备 GaN纳米线的形貌 （图 1在左中右三幅照片分别对应着 NH3流量的不同： 即分别为 50， 100和 200sccm。 生长温度： 550、 600和 650°C除纳米线径度外， 外观无显著区别。
图 2 为本发明实施例的产物照片。 HVPE生长 GaN纳米线的扫描电子显微镜照片， 其中插入图为高倍数照片。
具体实施方式
本发明方法和工艺包括几个部分:金属 Ni薄膜在蓝宝石衬底上的物理气相沉积; GaN 纳米线的 HVPE低温生长。
本发明技术实施方式之一， HVPE技术制备 GaN纳米线， 包括下面几步：
1、 蓝宝石衬底的清洗和处理。 将样品依次在去离子水、 乙醇和去离子水中进行 超声清洗， 除去表面残留的污染物， 用氮气吹干。
2、 蓝宝石衬底放入物理气相沉积装置反应腔内， 在一定反应腔体压力和金属源 温度下， 即可开始金属 Ni薄膜的蒸镀。 Ni薄膜沉积速率设置约为 1-2埃 /秒， Ni纳米薄膜厚度 5-50nm。 本实施例选择 20-30nm。
3、 将覆有金属镍薄膜的蓝宝石衬底放入 HVPE生长系统中， 开始低温生长 GaN 纳米线。 生长温度： 550、 600和 650 °C三个温度条件； 高纯 N2作为载气， 总 1^2载气流量 l-5slm; 高纯金属镓和高纯 HC1反应生成 GaCl作为镓源， HC1 流量： l-20sccm， HCl载气流量 10-200sccm。高纯氨气作为氮源， NH3流量（对 应三种流量）: 50， 100和 200sccm; 生长时间 5分钟。
4、 按照步骤 3生长完成后降温取出样品， 即获得 GaN纳米线。 控制步骤 2-4中的参数， 可以实现金属 Ni薄膜在纳米线生长温度时退火成有 序颗粒， 从而获得有序排列的 GaN纳米线。

Claims

权利要求书
1、 一种制备 GaN 纳米线的方法， 其特征是蓝宝石衬底清洗后， 先蒸镀金属 Ni 薄 膜； i镍薄膜厚度 5-50nm; 将覆有镍薄膜的蓝宝石衬底放入 HVPE 生长系统中， 开始低 温生长 GaN纳米线； 生长温度： 500-85CTC ; 高纯 N2作为载气， 总 N2载气流量 l-5slm; Ga源采用常规的高纯金属镓和高纯 HC1反应生成 GaCl， HC 流量： l-20sccm， HC1载气 流量 10-200sccm; 以高纯氨气作为氮源， NH3流量： 50-500sccm; 生长时间 1-10分钟。
2、 根据权利要求 1所述的用 HVPE生长 GaN纳米线， 其特征是， 生长温度是： 500- 650 °C。
PCT/CN2013/077974 2012-08-31 2013-06-26 一种GaN纳米线生长方法 WO2014032465A1 (zh)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN201210317228.4 2012-08-31
CN2012103172284A CN102828250A (zh) 2012-08-31 2012-08-31 一种GaN纳米线生长方法

Publications (1)

Publication Number Publication Date
WO2014032465A1 true WO2014032465A1 (zh) 2014-03-06

Family

ID=47331546

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2013/077974 WO2014032465A1 (zh) 2012-08-31 2013-06-26 一种GaN纳米线生长方法

Country Status (2)

Country Link
CN (1) CN102828250A (zh)
WO (1) WO2014032465A1 (zh)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107881554A (zh) * 2017-10-18 2018-04-06 中国科学院半导体研究所 在衬底上生长GaN平面纳米线的方法

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102828250A (zh) * 2012-08-31 2012-12-19 南京大学 一种GaN纳米线生长方法
CN103456602B (zh) * 2013-03-18 2016-12-07 深圳信息职业技术学院 非极性面氮化镓纳米锥材料的制备方法
CN107910243A (zh) * 2017-10-18 2018-04-13 中国科学院半导体研究所 在衬底上制备GaN纳米线的方法
CN110284198B (zh) * 2019-07-22 2020-11-10 南京大学 一种控制GaN纳米线结构与形貌的分子束外延生长方法

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008108757A (ja) * 2006-10-23 2008-05-08 Matsushita Electric Works Ltd 化合物半導体発光素子およびそれを用いる照明装置ならびに化合物半導体素子の製造方法
CN101229912A (zh) * 2007-12-26 2008-07-30 中国科学院上海微系统与信息技术研究所 采用干法刻蚀制备氮化镓纳米线阵列的方法
CN101510504A (zh) * 2009-03-13 2009-08-19 苏州纳晶光电有限公司 半导体薄膜的纳区横向外延生长方法
CN101689484A (zh) * 2007-07-10 2010-03-31 Nxp股份有限公司 失配衬底上的单晶生长
CN101898751A (zh) * 2009-05-27 2010-12-01 中国科学院半导体研究所 Ⅲ族氮化物纳米材料的生长方法
CN102828250A (zh) * 2012-08-31 2012-12-19 南京大学 一种GaN纳米线生长方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7438759B2 (en) * 2004-10-21 2008-10-21 Sharp Laboratories Of America, Inc. Ambient environment nanowire sensor
CN101728248A (zh) * 2008-10-15 2010-06-09 中国科学院半导体研究所 氮化镓生长方法
JP5359740B2 (ja) * 2009-09-29 2013-12-04 豊田合成株式会社 Ｉｉｉ族窒化物系化合物半導体の製造方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008108757A (ja) * 2006-10-23 2008-05-08 Matsushita Electric Works Ltd 化合物半導体発光素子およびそれを用いる照明装置ならびに化合物半導体素子の製造方法
CN101689484A (zh) * 2007-07-10 2010-03-31 Nxp股份有限公司 失配衬底上的单晶生长
CN101229912A (zh) * 2007-12-26 2008-07-30 中国科学院上海微系统与信息技术研究所 采用干法刻蚀制备氮化镓纳米线阵列的方法
CN101510504A (zh) * 2009-03-13 2009-08-19 苏州纳晶光电有限公司 半导体薄膜的纳区横向外延生长方法
CN101898751A (zh) * 2009-05-27 2010-12-01 中国科学院半导体研究所 Ⅲ族氮化物纳米材料的生长方法
CN102828250A (zh) * 2012-08-31 2012-12-19 南京大学 一种GaN纳米线生长方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107881554A (zh) * 2017-10-18 2018-04-06 中国科学院半导体研究所 在衬底上生长GaN平面纳米线的方法

Also Published As

Publication number Publication date
CN102828250A (zh) 2012-12-19

Similar Documents

Publication Publication Date Title
Kim et al. Fabrication of the hybrid ZnO LED structure grown on p-type GaN by metal organic chemical vapor deposition
Kente et al. Gallium nitride nanostructures: Synthesis, characterization and applications
TWI281709B (en) Method for fabrication of group III nitride semiconductor
CN106803478B (zh) 一种GaN纳米结构阵列生长方法
EP1883103A2 (en) Deposition of group III-nitrides on Ge
WO2014032465A1 (zh) 一种GaN纳米线生长方法
TW201344951A (zh) 外延結構
TWI320948B (en) Method for growing emiconductor crystal and laminated structure thereof and semiconductor device
TW201536669A (zh) 外延結構
WO2014032467A1 (zh) 一种制备低应力GaN薄膜的方法
CN104952984B (zh) 外延结构的制备方法
Ji et al. Understanding the 2D-material and substrate interaction during epitaxial growth towards successful remote epitaxy: a review
US20140162021A1 (en) Method for producing graphene, and graphene produced by the method
TWI557066B (zh) 外延結構的製備方法
WO2014032468A1 (zh) 一种制备GaN薄膜材料的方法
CN106757323B (zh) 一种无应力InN纳米线生长方法
JP2004307253A (ja) 半導体基板の製造方法
JP6271390B2 (ja) 窒化物半導体結晶成長方法
CN114678257A (zh) 一种基于金属衬底的氮化物模板及其制备方法和应用
Ngo et al. Field-Effect Transistor Behavior of Synthesized In 2 O 3/InP (100) Nanowires via the Vapor–Liquid–Solid Method
Ramesh et al. Influence of substrate nitridation on properties of GaN nanorods grown on molybdenum foil by laser molecular beam epitaxy
Olivier et al. Gallium nitride nanowires grown by low pressure chemical vapour deposition on silicon substrate
Tsai et al. Effects of temperature and nitradition on phase transformation of GaN quantum dots grown by droplet epitaxy
Kang et al. Synthesis of GaN nanowires and nanorods via self-growth mode control
WO2014040446A1 (zh) 一种InN基薄膜材料生长方法

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 13832976

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 13832976

Country of ref document: EP

Kind code of ref document: A1