Capacitance transient spectroscopy

Two deficiencies of the current-transient spectroscopy, as compared with the capacitance-transient spectroscopy, involve the determinations of the trap... 

A3.5 Time-resolved photoluminescence studies of GaN A3.6 Persistent photoconductivity in GaN A3.7 Electrical transport in wurtzite and zincblende GaN A3.8 Characterisation of III-V nitrides by capacitance transient spectroscopy... 

Capacitance transient spectroscopy encompasses a powerful set of techniques to detect and characterise deep levels in semiconductors. The list of techniques applied for III-V nitrides includes deep level transient spectroscopy (DLTS) [1,2], double correlation DLTS (DDLTS) [3], isothermal capacitance transient spectroscopy (ICTS) [2], photoemission capacitance transient spectroscopy (ODLTS) [4] and optical ICTS (OICTS) [5], This Datareview presents the current status of deep level studies by capacitance transient techniques for III-V nitrides. A brief introduction to the techniques is given, followed by an example that demonstrates the application of DLTS and DDLTS for Si-doped... 

A3.8 Characterisation of111-Vnitrides by capacitance transient spectroscopy D2 p-Type Mg-Doped GaN... 

I ICP ICP-RIE ICTS ID IDB IR interstitial inductively coupled plasma etching inductively-coupled-plasma reactive ion etching isothermal capacitance transient spectroscopy inversion domain inversion domain boundary infrared... 

ODENDOR ODLTS ODMR OICTS OLCAO OMVPE OSC optically detected electron nuclear double resonance optical deep level transient spectroscopy optically detected magnetic resonance optical isothermal capacitance transient spectroscopy orthogonalised linear combination of atomic orbitals organo-metallic vapour phase epitaxy on-surface-cracking... 

The most widely used of these methods in the study of a-Si H have been field-effect, capacitance, and deep level transient spectroscopy (DLTS) measurements. Capacitance measurements actually include quite a number of variations such as capacitance versus applied voltage (C- V), frequency (C- w), or temperature (C-T), and also several kinds of distinct capacitance profiling techniques. The technique referred to as DLTS normally includes both capacitance-transient as well as current-transient measurements and will also be used as a generic term for such recent variations as isothermal capacitance transient spectroscopy (ICTS), constant capacitance methods, and the like. 

There exist several variations of the capacitance-transient DLTS procedure described above. A couple of these that have been applied recently to the study of a-Si H are isothermal capacitance transient spectroscopy (ICTS)byOkushicrfl/.(1981,1982, and 1983) and the constant capacitance DLTS method (CC-DLTS) utilized by Johnson (1983). 

The depth of the doubly occupied dangling-bond centers, i.e., the ionization energy of the second electron at the dangling-bond center, is also estimated from other experiments. The value of E of 0.6 eV for a-Si H sample No. 519 agrees with that estimated from isothermal capacitance transient spectroscopy (ICTS) measurements by Okushi et al. (1982), i.e., 0.56 eV. The depth of singly occupied neutral dangling-bond centers cannot be estimated from the ODMR measurement. This level lies lower than the D level... 

Photoluminescence (PL) and EL spectroscopy can be used to determine the presence of traps. Other techniques include current voltage measurements, capacitance voltage measurements, capacitance transient spectroscopy, and admittance spectroscopy. Under favorite conditions, the identification of the nature of the trap is possible. 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

We now discuss some of the experimental aspects of temperature spectroscopy. Lang (1974) called his original method deep level transient spectroscopy (DLTS), and he measured capacitance transients produced by voltage pulses in diodes made from conductive materials. However, in SI materials, this method is not feasible and an alternate method, involving current transients produced by light pulses in bulk material (or Schottky structures), was... 

In Table IV we present Eai and Ei0 data on two important deep centers in GaAs, Cr, and O (EL2). The results from three different laboratories are included, but no attempt was made to show everything available in the literature. It is clear that neither the Eai results nor the Ei0 results agree well for Cr, but are not too bad for O. In contrast, the TDH measurements of El0, shown in Table II, are much more consistent. It should be noted that the TDH samples (Table II) were semi-insulating, whereas the emission-spectroscopy samples (Table IV) were conducting in order that capacitance transient (DLTS) experiments could be performed. The PITS and OTCS techniques applied to these samples would have been unable to clearly distinguish between hole and electron traps. 

Volume 21, Part C, is concerned with electronic and transport properties, including investigative techniques employing field effect, capacitance and deep level transient spectroscopy, nuclear and optically detected magnetic resonance, and electron spin resonance. Parameters and phenomena considered include electron densities, carrier mobilities and diffusion lengths, densities of states, surface effects, and the Staebler-Wronski effect. 

The first of these approaches is used in the technique of deep level transient spectroscopy (DLTS), which is perhaps the most common experiment for measuring deep levels in crystalline semiconductors (Lang 1974). The DLTS experiment is the measurement of the transient capacitance of a Schottky contact to the sample and is... 

In the following, we present the results of charge transient spectroscopy performed on the bottom contacted pentacene OFETs, a variant of DLTS where the current transient is integrated, yielding a charge transient [43, 44]. In combination with capacitance DLTS, this technique can also provide information on the depth profile of the trap distribution [45]. 

Deep levels can be described by the Shockley-Read-Hall recombination statistics [5]. However, for a large number of deep states, the capture cross section for one type of carrier is many times larger than that for the other carrier. The state, therefore, interacts principally with only one of the band edges and can be characterised as either an electron or a hole trap. Capacitance techniques, such as DLTS (Deep Level Transient Spectroscopy), are particularly convenient for the determination of trap type and concentration. If additional experimental information is present to allow charge state determination, then the states can be characterised as deep acceptors or donors. 

Fig. 42. Block diagram of apparatus for constant-capacitance, deep level transient spectroscopy. [From Johnson (1982).]...

One can use the PM technique with pulse excitations and study the time evolution of the spectra or the decay of the total oscillator strength of the bands. In this way one can obtain information about electronic relaxation processes. However, in this chapter we restrict ourselves to steady-state PM spectroscopy. We also note that instead of using illumination, the state occupation can be changed by changing the bias of a junction, as used in deep-level transient spectroscopy junction capacitance techniques. This method, dubbed charge-induced absorption, or CIA [44J, has already been used in conducting polymers and is discussed in another chapter of this book. 

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