Multi-microscopy nanoscale characterization of the doping profile in a hybrid Mg/Ge-doped tunnel junction

Abstract

A multi-microscopy investigation of a GaN tunnel junction (TJ) grown on an InGaN-based light emitting diode (LED) has been performed. The TJ consists of a heavily Ge-doped n-type GaN layer grown by ammonia-based molecular-beam epitaxy on a heavily Mg p-type GaN thin layer, grown by metalorganic vapor phase epitaxy. A correlation of atom probe tomography, electron holography and secondary ion mass spectrometry has been performed in order to investigate the nm-scale distribution of both Mg and Ge at the TJ. Experimental results reveal that Mg segregates at the TJ interface, and diffuses into the Ge-doped layer. As a result, the dopant concentration and distribution differ significantly from the nominal values. Despite this, electron holography reveals a TJ depletion width of ~7 nm, in agreement with band diagram simulations using the experimentally determined dopant distribution.

Behavior of the ε-Ga2O3:Sn Evaporation During Laser-Assisted Atom Probe Tomography

“…Lastly, very weak peaks associated with Ga 2 O 3 2+ cations appear in the interval of 84–89 Da. The presence of molecular ions was observed in mass spectra of several semiconductors (GaN, ZnO, GaAs, GaSb, InP, and InGaAs) (Müller et al, 2011; Mancini et al, 2014; Amirifar et al, 2015; Di Russo et al, 2017 a , 2017 b , 2018 a , 2020 b ; Cuduvally et al, 2020), and all these studies agree that their relative abundance increases at low-field conditions. In fact, high electric field conditions are more effective in breaking atomic bonds, leading to the evaporation of monoatomic ions rather than molecular ones.…”

“…Because no O–O bonds are present in the ε-Ga 2 O 3 :Sn structure, a massive presence of oxygen molecules in mass spectrum must be associated with chemical reactions occurring on the tip surface or with dissociative processes taking place just after the emission of larger cations, as it will be discussed later (Saxey, 2011; Gault et al, 2016; Di Russo et al, 2020 a , 2020 b ). Another five molecular ions were recognized here.…”

“…In the dataset analyzed, double and triple events correspond to the 14 and 6% of the total recorded events. However, it must be noted that such a remarkable percentage is limited by the active area of the micro-channel plate (MCP detection efficiency η MCP ≈ 0.6) that considerably reduces the detection efficiency of double and triple events to 0.36 and 0.22, respectively (Di Russo et al, 2020 a , 2020 b ).…”

“…In the last decade, laser-assisted atom probe tomography (La-APT) was widely employed in order to analyze the composition of dielectrics and semiconductors at the nanometer scale, including dopant atom distribution and chemical mapping of defects, providing fundamental new insights into the atom-scale mechanisms taking place during material growth and device fabrication (Grenier et al, 2014; Rigutti et al, 2016; Di Russo et al, 2017 a , 2017 b , 2020 a , 2020 b ; Dumas et al, 2019; Amichi et al, 2020; Cuduvally et al, 2020; Dimkou et al, 2020; Bougerol et al, 2021; Dumas et al, 2021). Such local quantitative analyses require to measure elemental composition with high accuracy (i.e., sensitivity in the range of 10 18 –10 19 cm 3 ) and near-atomic scale resolution.…”

“…Such local quantitative analyses require to measure elemental composition with high accuracy (i.e., sensitivity in the range of 10 18 –10 19 cm 3 ) and near-atomic scale resolution. In recent years, the reliability of APT measurements was systematically investigated for various high-technological interest semiconductor materials like nitrides (GaN, AlN, InN, AlGaN, and InGaN) and oxides (ZnO, MgO, and MgZnO) (Mancini et al, 2014; Amirifar et al, 2015; Di Russo et al, 2017 a , 2017 b , 2018 a , 2020 a , 2020 b ; Zanuttini et al, 2018). Surprisingly, all these studies reveal that APT measures nonstoichiometric compositions with 10% or more variations on the expected value of composition provided by more reliable analytic techniques (i.e., SIMS, RBS) or fixed by the material crystalline structure itself, as in the case of binary semiconductors like GaN or ZnO.…”