1 / 14

Introduction to DLTS (Deep Level Transient Spectroscopy) II. Advanced Techniques O. Breitenstein

Introduction to DLTS (Deep Level Transient Spectroscopy) II. Advanced Techniques O. Breitenstein MPI MSP Halle. Outline: 1. Basic principles Application field of DLTS Principles of DLTS Basic measurement techniques 2. Advanced techniques Advanced DLTS measurement techniques

justis
Download Presentation

Introduction to DLTS (Deep Level Transient Spectroscopy) II. Advanced Techniques O. Breitenstein

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to DLTS (Deep Level Transient Spectroscopy) II. Advanced Techniques O. Breitenstein MPI MSP Halle

  2. Outline: • 1. Basic principles • Application field of DLTS • Principles of DLTS • Basic measurement techniques • 2. Advanced techniques • Advanced DLTS measurement techniques • 3. (next time) Our DLTS system • - Philosophy • - Hardware • - User surface

  3. Recapitulation: DLTS routine (repeating!) : reverse reduced or forward reverse Vr bias t 0 e- e- e- band diagram e- e- RF- capacitance t DC 0 t

  4. DCmeas t t1 t2 t t2 t1 t t2 t1 DLTS signal = C(t1)-C(t2) Tpeak T DCpeak Generation of the DLTS signal opt. T low T high T "rate window": If T is slowly varying, at a certain temperature a DLTS peak occures

  5. ln(en) DLTS e01 e03 e02 e02 e03 e01 T T3 T2 T2 T1 T1 T3 1000/T DLTS measurements at different rate windows allow one to measure Et This "Arrhenius plot" allows an identification of a deep level defect

  6. h+ e- e- e- e- e- e- h+ e- e- e- e- xh h+ h+ h+ 2. Advanced DLTS measurement techniques 2.1. Possible samples: Schottky diodes or pn-junctions Schottky diode pn-junction reverse bias V = 0 xe forward bias minority carrier injection majority carrier flow

  7. Schottky diodes: • Standard, easy to prepare, high quality demand ! • Only majority carrier traps visible, even under forward bias • pn-junctions: • reverse bias reduction up to 0V: "majority carrier pulse" • forward bias (injection): "minority carrier pulse" (MC) • MC pulse may reveal both minority and majority carrier traps • However, if opposite carrier capture dominates, traps may remain uncharged (invisible in DLTS) => basic limitation ! • Asymmetric doping concentration: signal from lower doped side • Other sample types: • Grain boundary (anti-serial Schottky diodes) =>bonded wafers • MIS devices • FETs ("conductivity DLTS") • point contacts at nanowires ? ...

  8. e- h+ h+ e- e- h+ h+ h+ • 2.2. Optically excited DLTS (minority carrier DLTS, MCDLTS) • trap filling by optically excited minority carriers (hn > Eg) • reverse bias remains constant thermal equilibrium traps emptied (from holes) measurement hole emission filling pulse hole capture • allows investigation of minority carrier traps in Schottky diodes

  9. Tpeakillumin. T Tpeakdark T • 2.3. Optical DLTS (ODLTS) • trap filling by bias pulses • continuous irradiation of IR light (< Eg) • optical emission additional to thermal emission • strong dependence on intensity and l illuminated dark • ODLTS allows to measure optical capture cross sections sopt(l) • connection between deep levels electrically detected (DLTS) and optically detected (absorption)

  10. Tpeak T e- Tpeak e- T Tpeak e- T Tpeak e- T 2.4. Concentration depth profiling (pulse height scan) Vr t Vr t Vr t Vr t • linear dependence on Vp: homogeneous concentration !

  11. Tpeak1 T Tpeak2 T Tpeak3 T Tpeak4 T 2.5. Measurement of field dependence of en;p (pulse height scan) Vr t Vr • quantitative evaluation: difference spectra (DDLTS) • field depencence indicates charged occupied state t Vr t Vr t

  12. Tpeak T Tpeak T Tpeak T Tpeak T 2.6. Measurement of capture cross sections (pulse width scan) Vr t Vr t Vr • "real" capture cross section • measurement at different rate windows: T-dependence of CCS • injection: measurement of minority carrier CCS t Vr t

  13. e - e - e - e - 2.7. Point defects and extended defects • all previous considerations referred to isolated point defects • "extended defects": dislocations, grain boundaries, precipitates ... • continuum of states, "broadened states" • emission probability depends on average occupation state • barrier-controlled capture, depending on occupation state point defect extended defect DLTS low occupation T DLTS high occupation tc log(timp) • extended defects show logarithmic capture behaviour

  14. Summary • DLTS on Schottky diodes only reveals majority carrier taps • DLTS on pn junctions also reveals minority carrier traps • Optically excited DLRS (MCDLTS) also reveals minority carrier traps in Schottky diodes • ODLTS reveals optical trap parameters sopt(l) • There are special DLTS procedures for measuring: • - concentration depth profiles • - electric field dependence of en;p • - capture cross sections for electrons and holes • Extended defects are usually characterized by a logarithmic capture behaviour and often show non-exponential emission (broadened peaks) • Next time: Introduction of our own DLTS system

More Related