Tutorial: Junction spectroscopy techniques and deep-level defects in semiconductors

Abstract

The term junction spectroscopy embraces a wide range of techniques used to explore the properties of semiconductor materials and semiconductor devices. In this tutorial review we describe the most widely used junction spectroscopy approaches for characterizing deep-level defects in semiconductors and present some of the early work on which the principles of today's methodology are based. We outline ab-initio calculations of defect properties and give examples of how density functional theory in conjunction with formation energy and marker methods can be used to guide the interpretation of experimental results. We review recombination, generation and trapping of charge carriers associated with defects. We consider thermally driven emission and capture and describe the techniques of Deep Level Transient Spectroscopy (DLTS), high resolution Laplace DLTS, admittance spectroscopy and scanning DLTS. For the study of minority carrier related processes and wide gap materials we consider Minority Carrier Transient Spectroscopy (MCTS), Optical DLTS (ODLTS and DLOS) together with some of their many variants. Capacitance, current and conductance measurements enable carrier exchange processes associated with the defects to be detected. We explain how these methods are used in order to understand the behaviour of point defects, the determination of charge states and negative-U (Hubbard correlation energy) behaviour. We provide, or reference, examples from a wide range of materials including Si, SiGe, GaAs, GaP, GaN, InGaN, InAlN and ZnO.

Defect identification based on first-principles calculations for deep level transient spectroscopy

“…The difference in energy of the minima of the two curves is the thermodynamic charge-state transition level referenced to E v , and corresponds to the ionization energy ∆E i from Eq. (1). At high temperatures the capture process occurs by surmounting the "classical" barrier, 2 ∆E b , obtained from the intersection point of the curves in the configuration coordinate diagram; at low temperatures, the transition rate is dominated by quantum-mechanical tunneling.…”

“…Deep level transient spectroscopy (DLTS) is a powerful technique for determining the properties of defects; from an analysis of electrical measurements on a pn junction or Schottky diode, properties such as the position of the defect level within the band gap, electrical nature (donor or acceptor), density, and carrier capture cross section of specific defects can be obtained. [1][2][3] Translating this wealth of information to a microscopic identification of a given defect requires comparison with theoretical or computational models, and first-principles calculations based on density functional theory (DFT) have proven very helpful. [4][5][6][7][8] One of the key quantities measured in DLTS is the activation energy for carrier emission from a defect, ∆E a .…”

Acceptor levels of the carbon vacancy in 4H-SiC: Combining Laplace deep level transient spectroscopy with density functional modeling

“…While it was not possible to measure the temperaturedependence of the cross-sections (and respective barriers) for the first electron capture, the second capture showed barriers of ∆E σ = 65 meV and 80 meV for Z 1 and Z 2 , placing the (=/−) levels at E c −0.67 eV and E c −0.71 eV, respectively. 14 Due to resolution limitations, 20,21 separate emissions from Z = 1 and Z = 2 cannot not be resolved by conventional DLTS. To surmount this difficulty, activation energies and capture cross sections for Z 1 (= /−) and Z 2 (= /−) were estimated by fitting the data to biexponential capacitance transients subject to a fixed ratio between the two components (taken from the amplitude ratio of the first acceptors).…”

Minority Carrier Trap in n-Type 4H–SiC Schottky Barrier Diodes

“…Minority carriers in Schottky barrier diodes (SBDs) could be optically generated by use of above-bandgap light [6]. The first experimental application of the generation of minority carriers by use of a light with an energy just above the bandgap energy as a technique for manipulating the occupancy of deep states was described by Hamilton et al [7] and it was called the minority carrier capture (MCC) method.…”

“…It was further developed into minority carrier transient spectroscopy (MCTS) by Brunwin et al [8]. In addition to MCTS, a technique called optical-DLTS, in which the employed light has an energy below the bandgap energy, has been reported [6].…”