High-quality n-type conductive Si-doped AlInN/GaN DBRs with hydrogen cleaning

Abstract

We proposed and investigated a hydrogen cleaning for decreasing pits and threading dislocations generated at interfaces of GaN on AlInN in Si-doped graded AlInN/GaN DBRs. We found that the hydrogen cleaning was very useful to suppress the threading dislocation generations, resulting in two orders of magnitude less than the case without the hydrogen cleaning. A high-quality conductive Si-doped AlInN/GaN DBR was obtained with the hydrogen cleaning, showing the maximum reflectivity of 99.8 %, a low pit density less than 106 cm-2, and a reasonably low vertical resistance of 15 Ω.

N-type conducting AlInN/GaN distributed Bragg reflectors with AlGaN graded layers

“…Actually, in the hydrogen cleaning case without HT-AlGaN graded layer, the pit density of the 40-pair Si-doped AlInN/GaN DBR was less than 1.0 × 10 6 cm −2 . 18) Other factors related with a combination of many pairs of the DBR and a use of HT-AlGaN graded layers could be suspected, such as a tensile strain accumulation in the AlGaN graded layers as discussed later.…”

“…Note that this sequence (the very thin GaN cap layer growth on AlInN and the subsequent thermal cleaning) is identical to that of the high-quality undoped AlInN/GaN DBR, which is a key to reduce pit/TD densities generated at GaN/AlInN interfaces without any additional cleaning processes. 17) The surface pits should be originated from the TDs, 17,18) so we expressed "pit/TD" in this paper. The 5 nm AlGaN graded layers were then grown at 1150 °C, while the amounts of Al and Ga sources were adjusted to form the compositional graded layer from AlGaN to GaN toward the surface.…”

“…The key point for the high-quality DBRs was in situ AlInN surface cleaning in the MOVPE chamber. 17,18) We found that a very thin (0.3 nm) low-temperature-grown (LT-) GaN cap layer on AlInN at 840 °C and a subsequent cleaning process, regardless of thermal cleaning with a temperature increase up to 1100 °C17) or hydrogen cleaning with a 31 SLM flow, 18) suppressed threading dislocation (TD) generations at GaN/ AlInN interfaces. Note that the similar TD generations were observed in GaInN/GaN quantum wells possibly due to In-In bonds on the surfaces.…”

“…We have recently reported that a high-quality Si-doped n-type conducting AlInN/GaN DBR with LT-AlGaInN graded layers, showing a maximum reflectivity of 99.8% and a low surface pit density of less than 10 6 cm −2 . 18) So far, such high-quality conducting AlInN/GaN DBRs have been obtained only by hydrogen cleaning. In general, the conducting DBRs require graded layers at the interfaces, for instance, a 5 nm AlGaInN graded layer in the AlInN/GaN DBR case.…”

In situ cavity length control of GaN-based vertical-cavity surface-emitting lasers with in situ reflectivity spectra measurements

“…We used high-quality lattice-matched 40-pair AlInN/GaN DBRs grown by metalorganic vapor phase epitaxy (MOVPE) as a bottom DBR, showing a peak reflectivity of 99.8% and over. 32,33) We showed a temperature dependence of the center wavelength of the AlInN/GaN DBR and a reflectivity intensity oscillation at the resonance wavelength during the GaN-based cavity growth. We then demonstrated an accuracy of the in situ cavity length control within a 0.5% error.…”