Optical studies of non‐polar m‐plane () InGaN/GaN multi‐quantum wells grown on freestanding bulk GaN

Abstract

We report on the optical properties of non-polar m-plane InGaN/GaN multi-quantum wells (MQWs) grown on ammonothermal bulk GaN substrates. The low temperature continuous wave (CW) photoluminescence spectra are broad with a characteristic low energy tail. The majority of the emission bands decay with a time constant~300 ps, but detailed photoluminescence time decay and time resolved spectroscopy measurements revealed the existence of a distinct slowly decaying emission band. This slowly decaying component is responsible for the low energy tails observed in the CW spectra. Scanning electron microscopy-cathodoluminescence (SEM-CL) studies show that the low energy emission band originates from regions across step-bunches, which are associated to the GaN substrate miscut. Subsequent scanning transmission electron microscopy imaging demonstrates that semi-polar QWs had formed continuous layers on the step bunches between the m-plane QWs and were responsible for the slower decaying, low energy emission band. Thus we assign the asymmetric low energy emission tails observed in photoluminescence studies to the formation of semi-polar facet QWs across the step bunches associated with the GaN miscut.

Structural, electronic, and optical properties ofm-plane InGaN/GaN quantum wells: Insights from experiment and atomistic theory

“…The data reported by Marcinkevicius et al [44] at low temperature were shown to be not influenced by nonradiative recombination. Only on the low-energy side of the spectra did we find more slowly decaying emission as we have reported elsewhere [21]. The emission on the low-energy side is attributed to semipolar QWs at step bunches described above.…”

“…Also the intrinsic field leads to a spatial separation of electron and hole wave functions, causing a reduced radiative recombination rate [4,6], an effect that can be particularly undesirable for high-efficiency optoelectronic devices. To circumvent these effects arising from the intrinsic built-in fields, which fundamentally are caused by the growth along the polar c axis, significant research has been directed towards the fabrication of semi-and nonpolar structures [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In the case of semi-and nonpolar planes the c axis is at a nonvanishing angle with respect to the growth direction.…”

“…Experimental studies on c-plane (In,Ga)N/GaN QW systems reveal that random alloy fluctuations lead to carrier localization effects, which can dominate the electronic and optical properties of these structures [23,24]. Clear experimental indications of the importance of alloy fluctuations on the properties of nonpolar (In,Ga)N QWs have also been presented [16,21,22]. To fully understand the structural, electronic, and optical properties of nonpolar (In,Ga)N QWs requires the use of a range of advanced experimental and theoretical techniques.…”

The nature of carrier localisation in polar and nonpolar InGaN/GaN quantum wells

“…All the samples discussed here were grown by metalorganic chemical vapor deposition (MOCVD), the polar sample was grown on c plane sapphire using a quasi-two temperature growth methodology which we have described in detail elsewhere, 36 and the nonpolar m-plane sample was grown on freestanding bulk GaN as described in Ref. 37. Using a CW excitation power density of 6 W/cm 2 from a He/ Cd laser, the room temperature IQE was measured using the methodology 36 of comparing the ratio of the integrated photoluminescence (PL) intensity at room temperature and 10 K. The measured ratios were 10% and 20% for the c-plane and m-plane samples, respectively.…”

Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

“…Comprehensive details of the quasi-two temperature 30 growth schedule and structural details of this sample can be found elsewhere. 32 The polar sample is a c-plane InGaN/GaN single QW structure grown on a (0001) sapphire substrate with an In fraction of 0.15 and a thickness of 2.9 nm at a temperature of 750 C using a single temperature growth methodology. 33 The structural properties of the c-plane sample are further described in Ref.…”