Electrical characterization of InP/GaInP quantum dots by space charge spectroscopy

Abstract

An investigation of coherently grown InP quantum dots embedded in Ga0.5In0.5P by conventional space charge spectroscopy methods is reported. Deep level transient spectroscopy (DLTS) is used to obtain quantitative information on the electron emission from the dots. The applied field is found to significantly enhance the electron emission rates as seen by shifts in the peaks towards lower temperatures with increased field. Taking the field induced barrier lowering into account, the emission energy for the one electron ground state of the dot is determined as 240±10 meV. The correlation between the measured signal and the observed electron accumulation in capacitance–voltage measurements is clearly demonstrated. Further, studies of the electron emission when the average electron population in the dots was varied show that the emission energies are modified by the coulomb charging energy. Admittance measurements as a function of temperature, bias and frequency were also performed, and the results are qualitatively explained in terms of response from the dots. These observations are consistent with the effect of the signal frequency on the measured carrier concentration profile. To complete the picture and in order to distinguish the DLTS signature of the dots from that of the deep levels in GaInP, electron traps in the barrier material were also characterized. Two main electron traps, one with an activation energy of about 950 meV and the other having an activation energy of 450 meV, were present in all the samples.

Deep level transient capacitance measurements of GaSb self-assembled quantum dots

“…10 Lines in the DLTS spectra were also associated with defects in the vicinity of the dots, and some of the defects have displayed metastable behavior. 10 Coulomb charging and electric field stimulated emission have been reported for a DLTS line with an activation energy of 220 meV and identified as the one electron ground state in InP quantum dots embedded in Ga 0.5 In 0.5 P. 11,12 An activation energy of 100 meV has been reported for a quantum-confined electron level in In 0.5 Ga 0.5 As dots on GaAs. 13 Optical properties of GaSb QDs have been investigated by PL.…”

Electrical characterization of self-assembled In0.5Ga0.5As/GaAs quantum dots by deep level transient spectroscopy

“…From the relative DLTS peak height ∆C/C, the sheet density of electrons emitted from the QDs, n dot , can be estimated from ∆C/ C = n dot (L/2W 2 N D ), where L is the distance of the dotplane from the surface, W the depletion width, and N D the volume doping density in the barrier. 6 The estimated n dot of 2 × 10 10 cm -2 is lower than the density of dots (~1 × 10 11 cm -2 ) determined by AFM on an uncapped QD sample, which would imply that each dot possesses ~0.2 electron, on average. The 100-meV activation energy for trap D is reasonable for an electron QL; note that this value, combined with the PL emission at ~1.30 eV and the band gap of 1.51 eV for GaAs at 4 K, would predict a hole QL at ~110 meV above the GaAs valence band.…”

“…The QDs, self-assembled in a barrier (or matrix) material, with dimensions smaller than 100 nm, are formed by mismatch strain in the growing thin film; this process is known as the Stranski-Krastanow growth mode. [1][2][3] The occurrence of QDs in various material system has been investigated by different space charge spectroscopies, such as InAs/GaAs QDs by capacitance-voltage (C-V) spectroscopy, 4,5 InP/GaInP QDs by deep level transient spectroscopy (DLTS) and admittance spectroscopy, 6 InAs/GaAs QDs embedded in the active zone of a laser diode by DLTS, 7 and Ge/Si QDs by admittance spectroscopy. 8 In this letter, we present a DLTS investigation of the electronic structure of In 0.5 Ga 0.5 As QDs self-assembled in a n-GaAs barrier and report a quantum level (QL) of 100 meV below the GaAs conduction band edge for electrons in the structure.…”

Quantum well heterostructures studied by deep-level transient spectroscopy

“…Although these optical techniques are very useful, they provide little information on the exact position of quantum levels relative to the band structure of the host lattice. With deep level transient spectroscopy (DLTS), the thermal emission energy, which is closely related to the appropriate band offset, can be determined [1][2][3][4][5][6][7][8][9]. In addition, many-particle states of quantum dots determined by quantization and Coulomb charging can be studied by DLTS [10].…”