Carrier localization in InN/InGaN multiple-quantum wells with high In-content

Abstract

We study the carrier localization in InN/In 0.9 Ga 0.1 N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 lm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of $12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN. The extension of the operation wavelength of III-nitrides to the near-infrared (NIR) range is possible thanks to the growth of high-quality InN films displaying a bandgap energy close to 0.65 eV (1.9 lm) at room temperature (RT). The particular optical and electronic properties of this semiconductor have rendered it a subject of extensive research aimed at the development of devices for photovoltaics, optoelectronics (laser diodes and detectors), highspeed electronics, opto-chemical sensing, and terahertz applications.1 Furthermore, thanks to the close-to-resonant behavior at 1.5 lm and saturable absorption of InN with recovery times in the picosecond range, 2 this semiconductor has emerged as a promising choice for all-optical signal processing applications in optical communication networks.From this point of view, low-dimensional InN-based structures such as multi-quantum-wells (MQWs) 3-5 or quantum dots (QDs) 6,7 can improve the efficiency of NIR devices by tuning their operation wavelength through bandgap engineering. Furthermore, the improved carrier confinement should lead to an enhanced linear and nonlinear optical response at resonant wavelengths. In this sense, strong absorption saturation has been recently demonstrated in high-In content InN/InGaN MQWs at 1.55 lm.8 In this paper, we investigate the carrier localization in InN/InGaN MQW structures by means of temperature-dependent photoluminescence (PL) measurements and pump-probe spectroscopy at 1.55 lm. Our results show that a fivefold increase in luminescence efficiency can be obtained in these nanostructures compared to bulk InN. This is consistent with the observation of a longer carrier lifetime in the MQW structure over the bulk material.The samples under study were grown by plasma-assisted molecular-beam epitaxy (PAMBE) on 10-lm-thick GaN-onsapphire templates. The substrate temperature during growth was 450 C and the N-limited growth rate was fixed at 280 nm/h. The MQW structure, designed to have a quasiresonant interband transition at 1.55 lm, consists of 41 periods of InN/In 0.9 Ga 0.1 N QWs with well and barrier thickness of 4.5 nm and 7 nm, respectively. The growth of the MQW structure starts with an InN layer (4.5 nm) at the substrate/ MQW interface, which assures the relaxation of at least 90% of the lattice mismatch at the first interface, as verified in situ by reflective high-en...

High In-content InGaN layers synthesized by plasma-assisted molecular-beam epitaxy: Growth conditions, strain relaxation, and In incorporation kinetics

“…Values of Eloc1 = 105 meV (for T<100K) and Eloc2 = 12410 meV (for T>100K) are obtained for the samples under study, as summarized in Table II. The small localization energy is in the same order of magnitude than the obtained in bulk InN films grown by PAMBE [41].…”

“…The small localization energy is in the same order of magnitude than the obtained in bulk InN films grown by PAMBE. 41 The evolution of the emission peak energy as a function of temperature describes an S shape where the blue shift at intermediate temperatures is explained by the filling of potential valleys with different depths upon excitation. 42,43 For the quantification of these potential fluctuations, Eliseev et al 42 proposed a band-tail model assuming a Gaussian-like distribution of the density of states.…”

Waveguide saturable absorbers at 155 μm based on intraband transitions in GaN/AlN QDs

“…For this purpose, Naranjo et al explored the potential of InN films and InN/InGaN multi-quantum-well structures with interband transitions at 1.55 µm, by analyzing their third-order nonlinear susceptibility (χ (3) ) [11] and their nonlinear absorption [12]. For these structures, a minimum recovery time in the range of tens of ps can be achieved [13].…”

Widely power-tunable polarization-independent ultrafast mode-locked fiber laser using bulk InN as saturable absorber

“…It should be noted the absence of reverse saturation of the absorption in Fig. 1(b) Furthermore, a relaxation time 10 ps   has been measured in this material using the pumpand-probe technique [28]. This result is significantly slower than the relaxation time in InGaAs-based and graphene materials (below 1 ps [7,27]).…”