What Is DLTS?
An important goal in semiconductor technology is the reduction of intrinsic and process-induced defects in the crystalline, polycrystalline and amorphous layers which comprise all semiconductor devices. Defects arising from impurities, grain boundaries, interfaces, etc. result in the creation of traps which capture free electrons and holes. Even at very low concentrations these trapping centers can dramatically alter device performance.
Deep Level Transient Spectroscopy (DLTS) is an extremely versatile technique for the determination of virtually all parameters associated with traps including density, thermal cross selection, energy level and spacial profile.
By monitoring capacitance or current or charge transients produced by pulsing the semiconductor junction at different temperatures, a spectrum is generated which exhibits a peak for each deep level. The height of the peak is proportional to trap density, its sign allows one to distinguish between minority and majority traps and the position of the peak on the temperature axis leads to the determination of the fundamental parameters governing thermal emission and capture (activation energy and cross section). Application of the method has led to the discovery of new phenomena and has provided a unique tool for the understanding of materials processing for semiconductor devices.
Some Sula DLTS Features:
- Quick and sensitive survey method for monitoring electrically active defects in semiconductors.
- Detection and characterization of both bulk and interface traps.
- Determination of defect densities, activation energies, thermal cross sections, spatial profiles, capture and emission rates.
- Sample types: p-n junctions, Schottky diodes, MOS structures, LEDs, FETs, semiconductor lasers, high-resistivity and semi-insulating materials.
- High sensitivity: detection of bulk traps at densities below < 109 atoms/cm3.
- Measurement modes include: C-V, C-T, I-V, I-T, DLTS, DDLTS, CCDLTS, DDLTS/CCDLTS, CTS, ITS, PICTS, QTS, Fast Pulse Interface, High Voltage Interface & Multiple Correlation.
- Modular design allows custom configurations and facilitates incorporation of new functions.
- Proprietary Capacitance Meter offers 3 microsecond response time, rapid recovery from overload and high immunity to leakage currents.
- Automatic suppression of background capacitance by 60 dB.
- Monitoring of sample leakage current during temperature sweeps.
- Rapid temperature scans: 100K in 8 minutes.
- Wide temperature ranges: 10K to 800K.
- Simultaneous generation up to 8 spectra with different rate windows during a single temperature scan.
- Digital acquisition includes 16-bit resolution, 1 microsecond sampling increments, a 5-decade time span and no limit to the number of averaged transients.
- Experimental Parameters and Processes Under Computer Control:
- Pulse Amplitude, Pulse Width, Pulse Period and DC Offset.
- Rate Window settings.
- Initial Temperature, Final Temperature, Temperature Increment and Sweep Rate.
- Data Acquisition Rate & Number of Averaged Transients.
- Graphical presentation details.
- Storage, plotting and analysis of spectra - including peak resolution improvement.
- Exporting experimental results to spread sheet files for future
numerical analyses.