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Investigation of optical properties of InGaN multiple quantum wellson free-standing GaN substrates grown by metalorganic vapor

phase epitaxy

Akihito Ohno,Nobuyuki Tomita,Tomoo Yamada,Hiroaki Okagawa, Masayoshi Takemi

Outline

IntroductionExperimentResults and DiscussionsConclusionsReferences

Introduction

In this paper, we report on temperature dependence of photoluminescence (PL) from InGaN MQWs on free-standing GaN substrates. PL properties for InGaN MQWs grown on sapphire substrates are also investigated for comparison.

Experiment

GaN substratesGaN substrates

500nm u-GaN500nm u-GaNMQWMQW

P-GaNP-GaNPP

NN3.5nm In0.12Ga0.88N-well7.0nm In0.02Ga0.98N-Barrier

Sample A->740 ℃ B->780 ℃ C->800 ℃

Sapphire substratesSapphire substrates

33 μ μ m u-GaNm u-GaNMQWMQW

P-GaNP-GaNPP

NN

20nm GaN buffer20nm GaN buffer

Sample D->720 ℃ E->750 ℃ F->770 ℃

Results and Discussions

Fig. 1. PL spectra at 5K for InGaN MQW grown at (a) 740 , (b) 780 and (c) 800 .℃ ℃ ℃

3.08 eV

3.09 eV 3.12 eV

低溫電激發螢光量測

Fig. 2. Temperature dependence of PL peak shift for InGaN MQW on GaN substrates grown at Tg of 740, 780 and 800 ℃.

主要是因為在高銦濃度的量子井中有較強的壓電場，使得量子侷限史塔克效應較大。而隨著溫度的上昇，載子得到能量跳出區域侷限能階，於是出現兩段不同程度的衰減情形。

氮化銦 e31= - 0.57 C/m2

氮化鎵 e31= - 0.49 C/m2

壓電場

Fig. 3. Temperature dependence of normalized integrated PL intensity for InGaN MQW on GaN substrates grown at Tg of 740, 780 and 800 ℃.

Fig. 5. Temperature dependence of normalized integrated PL intensity for InGaN MQW on sapphire substrates grown at Tg of 720, 750 and 770 ℃.

on sapphire substrates

Fig.4. Schematic in-plane energy band diagram for InGaN layer grown at (a) 740 ℃ and (b) 800 ℃.

在低溫高電流注入時，電洞會因溫度變化造成載子濃度及遷移率下降，使電洞在量子井中的分佈不均，且電洞的遷移率下降，電洞無法有效的注入量子井中累積在靠近 p-GaN的量子井中，而量子井中電洞不足，使電子會有溢流現象，導致內部量子效率遽降。

Conclusions

Tg from 740 to 800 ℃ ， found that measurement temperature dependence of the PL integralintensity for the InGaN MQW grown on free-standing GaN substrates is strongly influenced by Tg. The largest decreases both in energy and in intensity of the PL with increasing measurement temperature were observed for the sample grown at 800 .℃

Investigate the influence of TD density on optical properties of InGaN MQWs, we measured the temperature dependence of the PL from InGaN MQWs grown on the sapphire substrates (TDs108cm2). It became clear that growth temperature did not affect significant change to the PL properties of the MQWs on the sapphire substrates.

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