Compensation effects of high oxygen levels in semipolar AlGaN electron blocking layers and their mitigation via growth optimization

• Published in: Journal of crystal growth 2019-02, Vol.507 (C), p.118-123
• Main Authors: Becerra, Daniel L., Cohen, Daniel A., Mehari, Shlomo, DenBaars, Steven P., Nakamura, Shuji
• Format: Article
• Language: English
• Subjects: A1. Impurities; A3. Metalorganic chemical vapor deposition; Aluminum gallium nitrides; B1. Nitrides; B2. Semiconducting aluminum compounds; B3. Laser diodes; Compensation; Crystallography; Efficiency; Gallium nitrides; Materials Science; Metalorganic chemical vapor deposition; Optimization; Organic chemistry; Oxygen; Physics; Secondary ion mass spectroscopy; Semiconductor lasers; Threshold currents
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2018.11.008

•The p-AlGaN EBL in semipolar GaN LDs has a high [O] level suggesting compensation.•Growth optimizations reduced the [O] level.•Laser diodes were fabricated to study the impacts of the reduction of oxygen.•The laser diodes with low oxygen showed improved properties.•Internal loss and gain measurements confirm an injection efficiency improvement. InGaN-based laser diodes (LDs) grown on the semipolar (202¯1¯) plane of GaN offer advantages arising from predicted higher gain compared to c-plane devices. However, the performance of semipolar devices has been limited by low injection efficiency. In prior work, this has been proposed to be caused by an inefficient AlGaN electron blocking layer (EBL). A high oxygen level in the EBL found in previous work could cause compensation of the p-type dopants. In this work the oxygen impurities were eliminated via optimizations during the metalorganic chemical vapor deposition (MOCVD) growth. Optimization of the V/III ratio and an increase in the growth temperature during the AlGaN growth was found to reduce the oxygen incorporation. Additionally, residual sources of oxygen were removed from the MOCVD growth process. These combined steps reduced the peak oxygen level in the AlGaN from 5 × 1018/cm3 to 6 × 1017/cm3 as measured by secondary ion mass spectroscopy. LDs were fabricated with and without these modifications to clarify the effect of the reduced oxygen. The threshold current and differential efficiency showed improvement with reduced oxygen. The internal loss and gain of these LDs were measured using the segmented contact method, confirming that the injection efficiency was boosted from 60% with high oxygen to 80% with low oxygen.