Nature of electron trap states under inversion at In0.53Ga0.47As/Al2O3 interfaces

Abstract

In and Ga impurities substitutional to Al in the oxide layer resulting from diffusion out of the substrate are identified as candidates for electron traps under inversion at In 0.53 Ga 0.47 As/Al 2 O 3 interfaces. Through density-functional calculations, these defects are found to be thermodynamically stable in amorphous Al 2 O 3 and to be able to capture two electrons in a dangling bond upon breaking bonds with neighboring O atoms. Through a band alignment based on hybrid functional calculations, it is inferred that the corresponding defect levels lie at ∼1 eV above the conduction band minimum of In 0.53 Ga 0.47 As, in agreement with measured defect densities. These results support the technological importance of avoiding cation diffusion into the oxide layer.The microelectronic industry is investigating high mobility semiconductors for replacing silicon as substrate material. Among the III-V compounds, the In x Ga 1−x As family has gathered large interest for application in n-type devices.1 In particular, the compound In 0.53 Ga 0.47 As (here referred to as InGaAs) has suitable electronic properties for microelectronic devices and can easily be grown onto InP substrates.1,2 Amorphous Al 2 O 3 is the preferred dielectric owing to its wide bandgap, high breakdown field, and high thermal stability. 2Several passivation procedures have been considered to reduce the high density of interfacial defect states occurring at III-V/oxide interfaces (D it ).3-7 The origin of these states has been for long debated and recently assigned to As-As dimer bonds. [8][9][10][11][12][13] In addition to these interfacial states, a high density of oxide traps (D ot ) has recently been detected in the oxide layer of metal-oxide-semiconductor (MOS) devices. Capacitancevoltage (CV) measurements show a bimodal distribution for the density of defect states in the oxide, 14 with one peak at 1.5 eV above and the other at 0.5 eV below the CBM of InGaAs. Similarly, through positive bias temperature instability (PBTI) experiments, a wide distribution of defect states centered at about 1 eV above the InGaAs conduction band maximum (CBM) has been inferred.15 These states are considered to be at the origin of the degradation of the electrical properties, thereby compromising the performance of the corresponding MOS devices.14,15 Indeed, upon reaching the inversion of carrier population, the Fermi energy is pushed deep into the conduction band of InGaAs in order to achieve high carrier concentrations, and is then susceptible to defects in the upper part of the oxide band gap. The atomic origin of these defects has remained elusive. A hint might come from electrical measurements on InGaAs/Al 2 O 3 and Ge/GeO x /Al 2 O 3 interfaces which yield similar field acceleration factors, 16 but an assessment concerning the nature of the involved defects remains out of reach on this basis. More indicatively, a) Electronic mail: davide.colleoni@epfl.ch time-of-flight secondary ion mass spectroscopy studies on GaAs/Al 2 O 3 and InGaAs/Al 2 O 3 interfaces revea...

Electron trap states at InGaAs/oxide interfaces under inversion through constant Fermi-levelab initiomolecular dynamics

“…We model the structure at the interface through an amorphous substoichiometric system, of which the structure is generated by setting the Fermi-level above the CBM. As a result, we recover In and Ga atoms carrying doubly occupied DBs and As-As dimer/DB defects, as reported previously in the literature [29,31,35]. In addition, our scheme reveals the existence of a high fraction of metallic In-In, In-Ga, and Ga-Ga bonds.…”

“…Candidate defect states include In and Ga dangling bonds [25] and the antibonding state of the As-As dimer [3,28]. Recently, Colleoni et al have suggested that these states result from isovalent In and Ga impurities substitutional to Al in amorphous Al 2 O 3 oxide, giving rise to defect levels at ≈1 eV above the CBM of InGaAs, in agreement with the experimental characterization [31]. However, this study did not address all possible defect structures in an exhaustive way, due to the inherent limitation of the employed methodology, which mainly rests on educated guesses and physical intuition.…”

“…Second, the system tends to form a larger fraction of atoms carrying DBs. The formation of occupied DBs on In and Ga atoms upon capture of two electrons had already been identified in [31] as one possible charge trapping mechanism at energies above the CBM [31]. While these defects were identified by physical intuition in [31], they emerge directly as the result of the applied simulation method in the present work.…”

“…The formation of occupied DBs on In and Ga atoms upon capture of two electrons had already been identified in [31] as one possible charge trapping mechanism at energies above the CBM [31]. While these defects were identified by physical intuition in [31], they emerge directly as the result of the applied simulation method in the present work. Focusing on the local environment around As atoms, we infer that the decrease in the first peak of g AsAs (r) results from the reduction of the fraction of As atoms belonging to homopolar bonds.…”

“…We investigate the occurrence of defect states due to metallicbond impurities in Al 2 O 3 to evaluate their electrical activity in In 0.53 Ga 0.47 As devices. To this end, we take advantage of the accurate band alignment at the In 0.53 Ga 0.47 As/Al 2 O 3 interface achieved in [31].…”