A strategy for efficient p-doping in Al-rich AlGaN

Solving the doping asymmetry issue in wide-gap semiconductors is a long-standing challenge for device applications. Taking AlGaN as an example, it has preferable n-type conductivity, but requires immense efforts to achieve p-type one since its valence bands are relatively far from the vacuum level. This issue severely restricts the development of devices, typically AlGaN-based deep-ultraviolet optoelectronic ones, which have attracted much attention in the field of public and personal sterilization owing to their advantages of high efficiency, environment friendly, and portability, especially in the shadow of COVID-19.

 

In a new paper published in Light Science & Application, a team of scientists, led by Professor Bo Shen and Professor Fujun Xu from State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Peking University, China, have developed a desorption-tailoring strategy to realize efficient p-doping in Al-rich AlGaN. Self-assembled p-AlGaN superlattices with an average Al composition over 50% are prepared by adopting this approach, where the thickness of barriers remains constant at 3 monolayers (about 0.75 nm for AlGaN). Based on the significant reduction of the acceptor activation energy as well as the substantial enhancement of Mg surface-incorporation, the hole concentration as high as 8.1×10¹⁸ cm^-3 is realized at room temperature. More importantly, beneficial from the sub-nanometer ultrathin barrier thickness, the vertical miniband transport of holes is verified in the p-AlGaN SLs, greatly satisfying the demand of hole injection in devices. As an application, 280 nm DUV-LEDs are fabricated with the desorption-tailored Al-rich p-AlGaN SLs, whose light output power reaches 17.7 mW at 100 mA.

 

These scientists summarize the principle of their strategy:

“The key in this strategy is to steadily prepare sub-nanometer ultrathin barriers by MOCVD, it is difficult, in particular for ternary AlGaN. The desorption process during AlGaN growth is fully utilized here, and the thickness of the desorption layers is verified to remain constant (3MLs) in a large range of initial Al composition, desorption temperature and time, which guarantees the formation of minibands.”

 

“The high hole concentration is attributed to the significant reduction of effective Mg activation energy to 17.5 meV through modulating the activating path, as well as the highlighted Mg surface-incorporation by intentional interruption for desorption.” they added.

 

“This study provides a solution for p-type doping of Al-rich AlGaN, and also sheds light on solving the doping asymmetry issue in general for wide-gap semiconductors. Moreover, the preparation of sub-nanometer layers can be widely used in electronic and optoelectronic devices.” the scientists forecast.

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