Potential of Graphene as a Mask and Controllability for Hole Density = 그래핀의 마스크로의 활용 가능성과 구멍 밀도의 조절 가능성에 관한 연구

다국어 초록 (Multilingual Abstract)

This thesis introduce Graphene as novel mask material that can ultimately help
growing high quality GaN inspect of decreasing threading dislocation (TD) than
using other mask material. In prior studies, it is clearly confirmed that mask
material can decrease specific defect called threading dislocation (TD) by the
Epitaxial Lateral Overgrowth (ELO) method. This ELO method demand mask
material with hole that GaN growing through. As above statement, hole can help
decreasing TD density of GaN. In ELO method, the size of hole is important
factor that can determine TD density. Generally, smaller size hole can help more
decreasing TD density of GaN. Patterning method use mask material that
underwent lithography for hole. Lithography method has difficulty in control the
size of hole under specific size and the cost for lithography is set in high level. So,
recent studies introduce thru-hole method that using 2d materials as mask material
with smaller hole than lithography method. However, it is difficult to control
thru-hole of 2d mask material. Because when using chemical vapor deposition
(CVD), 2d material deposition process is very sensitive with deposition condition
such as pressure, temperature, gas flow. To overcome those difficulty, we used
Graphene as 2d mask material with oxygen plasma etching process. Surface of
Graphene can be easily etched by oxygen plasma process. By changing etching
condition, Graphene can be etched in various form in deliberate way. So the size
of the thru-hole can be much smaller than hole generated from lithography
method and thru-hole density can be more easily controlled than manipulating it
by depositing 2d materials by changing the generation time of oxygen plasma on
Graphene mask. There are few conditions are needed for Graphene to work as
controllable mask material: The coverage and uniformity of Graphene, proper
etching condition for make a thru-hole on Graphene. In this thesis, We
demonstrated conditions for the graphene work as mask material and also analyze
the evidence that show the controllability of thru-hole on Graphene.

목차 (Table of Contents)

• I. Introduction 1
• 1) Research history of GaN 1
• 2) GaN growth on sapphire substrate 3
• 3) Efficient tool for growing GaN on sapphire: thru-hole epitaxy 5
• 4) Graphene as a Mask material 7
• II. Theoretical background 8
• 1) c-oriented GaN 8
• 2) Threading dislocation (TD) 11
• 3) ELO (Epitaxial Lateral Overgrowth) 15
• 4) THE (Thru-Hole Epitaxy) 19
• 5) Thru-hole estimation method: Domain numbering 22
• III. Experiment 25
• 1) Graphene mask deposition (CVD) 25
• 2) Thru-hole generating process (Oxygen plasma) 28
• 3) GaN growth through HVPE 31
• IV. Results 35
• 1) Deposition of mask material (graphene) 35
• 2) Graphene etching process 38
• 3) Graphene quantity transition in GaN process 41
• 4) Change of thru-hole density of graphene 43
• V. Conclusion 46
• VI. References 47