Diagnostics of nanoheterostructures by admittance methods

Head of the laboratory: Prof. A.V. Zubkov

Advanced methods of heterostructure characterization are of vital importance for modern high-tech fabrication of ultra bright light-emitted diodes based on InGaN/GaN-MQW. Created in SPb ETU resource center is devoted to diagnostics of AIIIBV and AIIIN heterostructures by various electrical and optical methods, including admittance spectroscopy, luminescence, electrochemical profiling and atomic-force microscopy.

Admittance is a complex value consisted of an imagine part (proportional to capacitance) and a real part (proportional to conductance, or simply current). So, admittance spectroscopy combines advantages of both capacitance and current technics.

By scanning different electric parameters of p-n junction or Schottky barrier, available in admittance measurements, as function of temperature, applied bias and the frequency of the bias, one can propose a wide set of methods for precise quantitative characterization of semiconductor materials and structures.

Computer-controlled admittance setup

  • RLC-meter Agilent E4980A;
  • Closed-cycle helium probe station Janis CCR10-2-(2CXKEL-4PORTS);
  • Temperature controller LakeShore 336.
  • Only one temperature scan is needed for full database obtaining.
  • Parameters:
    • temperature range 15 – 475 К
    • frequency 20 Hz – 2 MHz
    • bias ± 40 V.
  • Precision 0.1 K in temperature.
  • 2” diameter sample mount.
  • 5 mkm positioning of tips.

Scanning probe microscopy

STM / AFM (contact + semi contact + non-contact)/ Kelvin Probe Microscopy/ Spreading Resistance Imaging/ Lithography: AFM (Voltage + Force), and other modes.

Electrochemical profilometer ECV Pro Nanometrics

  • Materials Measured: III-V, III-Nitrides, II-VI, Si, SiC;
  • Carrier concentration 1013 – 1020 cm-3;
  • Depth range 0.05 μm – 50 μm;
  • Depth resolution 1 nm;
  • Two-stage measurements: pulsed oxidation and etching;
  • 200W Hg-Xe UV lamp;
  • Carrier concentration distribution over a GaAs substrate.

Objects under tests (p-n and Schottky)

Materials and structures for nano- and optoelectronics (red & IR lasers; blue & white LEDs): heterojunctions (AlGaAs/GaAs, InGaAs/GaAs), quantum wells (InGaAs/ GaAs, InGaN/GaN), quantum dots (InGaAs/GaAs), QD wetting layers (InAs/GaAs).

Theoretical analysis

Originally created numerical self-consistent solution of Schrödinger and Poisson equations for simulation of carrier distribution in heterostructures with QW and MQW.

Extracted parameters of QWs

Lineup of conduction (valence) band edges, energy levels vs bias and QW composition, carrier concentration in subbands, band offsets in QW.