Influence from free-carrier tails in deep level transient spectroscopy (DLTS)

DLTS spectra of deep level impurities in semiconductors often display anomalies such as zero offsets, steps or peaks with reversed signs. For a correct interpretation of the spectra it is important to understand those features. They are explained here, and shown to be related to the presence of free-carrier tails which extend into the depletion region of a semiconductor junction. Gold-doped silicon and the so-called A- and B-levels in GaAs are chosen for illustration of the effects.     

A study of interface characteristics in HfAlO/p-Si by deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) and high-frequency capacitance-voltage (HF-CV) measurement are used for the investigation of HfAlO/p-Si interface. The so-called “slow” interface states detected by HF-CV are obtained to be 2.68 × 10¹¹ cm⁻². Combined conventional DLTS with insufficient-filling DLTS (IF-DLTS), the true energy level position of interfacial traps is found to be 0.33 eV above the valance band maximum of silicon, and the density of such “fast” interfacial traps is 1.91 × 10¹² cm⁻² eV⁻¹. The variation of energy level position of such traps with different annealing temperatures indicates the origin of these traps may be the oxide-related traps very close to the HfAlO/Si interface. The interfacial traps’ passivation and depassivation effect of postannealing in forming gas are shown by comparing samples annealed at different temperatures.     

Self-consistent tight-binding total energy calculations: Application to GaAs/Si and ZnSe/GaAs (100) interfaces

Self-consistent tight-binding total energy calculations are performed for various models of GaAs/Si and ZnSe/GaAs (100) interfaces. A graded GaAs/Si interface with the first monolayer on substrate having 1 As atom per 3 Si atoms followed by a second monolayer with 3 Ga atoms per 1 Si atom and continued with 2 bulk-like As and Ga monolayers is found to be structurally more stable than other interfaces. The instability of the abrupt interface is driven by elastic rather than electrostatic forces. Similar results are obtained for the ZnSe/GaAs (100) interface. The graded interface with Ga atoms exchanged against Zn atoms is found to be energetically most stable. Strong macroscopic electric fields are found in the surface and interface regions for both the GaAs/Si and ZnSe/GaAs interfaces.     

Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy

In this study deep level transient spectroscopy has been performed on boron–nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N_A–N_D)∼3×10¹⁷ cm⁻³. We observed a hole H₁ majority carrier and an electron E₁ minority carrier traps in the device having activation energies E_v+0.24 eV, E_c −0.41 eV, respectively. The capture cross-section and trap concentration of H₁ and E₁ levels were found to be (5×10⁻¹⁹ cm², 2×10¹⁵ cm⁻³) and (1.6×10⁻¹⁶ cm², 3×10¹⁵ cm⁻³), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H₁ defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E₁ defect to a nitrogen donor.     

W(100) reconstruction studied by core level spectroscopy

We compare the hydrogen and thermally induced reconstructions of W(100) by means of surface core level spectroscopy and analyse the energy positions of the spectral lines in the framework of existing theoretical models. Surprisingly, our results for both reconstructions differ more than would be expected from previous admitted structural models.     

Laplace deep level transient spectroscopy: Embodiment and evolution

This paper is to commemorate the work of Leszek Dobaczewski¹ who devoted much of his life to the development and application of high resolution DLTS.     

Study of metal-semiconductor interface states using deep level transient spectroscopy

This paper describes the principle of the determination of interface-state parameters by deep level transient spectroscopy (DLTS) and presents a new, simple and exact method to discriminate the DLTS signal due to the emission from interface states from that from bulk traps. The n-type Au-GaAs and Cr-GaAs interfaces have been investigated by the technique. The results obtained in the investigation have revealed the dependences of the energy position, density and capture cross section for the interface states on the metal deposited onto the semiconductor surface, which is consistent with the theoretical prediction by Yndurain and the experimental results obtained by other authors.     

Characterisation of defects in rare earth implanted GaN by deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) was used to investigate the electrical properties of GaN implanted with the rare earth (RE) ions erbium and thulium. The GaN layers have been grown by metal-organic chemical vapor deposition (MOCVD) onto (0001) sapphire substrates. We used the channeled implantation geometry to implant a dose of 5×10¹⁴ RE cm⁻² with an energy of 150 keV. For each species, two different annealing procedures were used in a nitrogen atmosphere for 120 s. Indeed, the annealing temperature plays an important role in the lattice recovery, even if RE-related defects remain present. After annealing at 1000 C, the appearance of two new peaks, for both studied RE ions, is associated with the lattice damage induced by the implantation, such as the presence of nitrogen vacancies. After annealing at 1100 C, the recovery of the lattice is observed while a hole trap appears for both implanted RE ions with corresponding energy values E_v+0.61 eV and E_v+1.59 eV, in the case of Er and Tm, respectively.     

A study of deformation-produced deep levels inn-GaAs using deep level transient capacitance spectroscopy

Deformation-produced deep levels, both of electron and hole traps, have been studied using deep level transient capacitance spectroscopy (DLTS) for an undopedn-type GaAs (HB grown) compressed at 440°C. Concentrations of two grown-in electron trap levels (E _c −0.65eV andE _c −0.74eV) and one grown-in hole trap level (E _v +∼0.4eV) increase with plastic deformation, while that of a grown-in electron trap level (E _c −∼0.3eV) decreases in an early stage of deformation. While no new peak appeared in the electron trap DLTS spectrum after plastic deformation, in the hole trap DLTS spectrum a broad spectrum, seemingly composed of many peaks, newly appeared in a middle temperature range, which may be attributed to electronic energy levels of dislocations with various characters.     

Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure

Deep level transient spectroscopy(DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors(HEMTs) has been widely utilized.The DLTS measurements under different bias conditions are carried out in this paper.Two hole-like traps with active energies of E_v + 0.47 eV,and E_v + 0.10 eV are observed,which are related to surface states.The electron traps with active energies of E_c-0.56 eV are located in the channel,those with E_c-0.33 eV and E_c-0.88 eV are located in the AlGaN layer.The presence of surface states has a strong influence on the detection of electron traps,especially when the electron traps are low in density.The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state.     

Photoemission study of alkali/GaAs(110) interfaces

A detailed core-level photoemission study of interfaces between thin alkali films andn-orp-type GaAs (110) formed at different substrate temperatures 85 K and 300 K) is reported. All the interfaces grown at 85 K (with Na, K, Rb, and Cs) were found to be non-reactive, while at 300 K, the interface with Na is reactive and that with Cs remains non-reactive. In case of the non-reactive interfaces, a strong band bending of 1.0 eV is observed forp-GaAs at alkali coverages as low as 0.01 monolayers, but practically none forn-GaAs. This striking asymmetry in band bending is interpreted as a consequence of the donor character of the alkali atoms. On the other hand, an approximately symmetric band bending at low coverages is observed for the reactive interfaces of Na withn- andp-GaAs and assigned to defect states. For high alkali coverages (>2 monolayers), the final band bending is characterizeds by the same Fermilevel position forn- andp-GaAs, independent of the reactivity of the interface, and assigned to metal-induced gap states. Furthermore, systematic trends along the alkali series in Fermi-level position ionization energy, plasmon-loss features, and layer-dependent binding-energy shifts of alkali core levels are discussed.     

High-resolution electron energy-loss spectroscopy at epitaxially grown GaAs(100)

High-Resolution Electron Energy-Loss Spectroscopy (HREELS) is shown to be a very sensitive tool to investigate the space-charge regime of n-respectively p-type semiconductors. The most simple model we applied to fit experimental spectra is based on a step-like distribution of free carriers with the Drude dielectric response function. In this case, the dispersion of surface plasmon excitations is neglected, but it is considered in the Thomas-Fermi and the Debye-Hückel models. We use these models to fit HREELS-spectra, obtained from heavily Si-doped GaAs(100), which was grown by Molecular Beam Epitaxy (MBE). A comparison shown that the Drude model overestimates both the free-carrier concentration and the plasmon damping factor. The use of a more realistic smooth free-carrier profile, obtained by the self-consistent solution of the Schrödinger and Poisson equations, leads to plasmon excitations with lower frequencies. Besides Ohmic damping, the calculations show that Landau damping should be incorporated in order to obtain a better fit, particularly at intermediate frequencies.     

GaAs/AlAs super-flat interfaces in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells grown on (4 1 1)A GaAs substrates by MBE

Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs) (AlAs) QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width ( ) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs) (AlAs) QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs) (AlAs) QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7 7 mm ), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs) (AlAs) QWs grown on the (4 1 1)A GaAs substrates.     

Electronic properties and deep level transient spectroscopy of CdS/CdTe thin film solar cells

It is well known that preparing temperatures and defects are highly related to deep-level impurities. In our studies, the CdTe polycrystalline films have been prepared at various temperatures by close spaced sublimation (CSS). The different preparing temperature effects on CdS/CdTe solar cells and deep-level impurities have been investigated by I--V and C--V measurements and deep level transient spectroscopy (DLTS). By comparison, less dark saturated current density, higher carrier concentration, and better photovoltaic performance are demonstrated in a 580oC sample. Also there is less deep-level impurity recombination, because the lower hole trap concentration is present in this sample. In addition, three deep levels, E_v+0.341 eV(H4), E_v+0.226 eV(H5) and E_C-0.147 eV(E3), are found in the 580oC sample, and the possible source of deep levels is analysed and discussed.     

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at E_v+0.128~eV, originates from the vacancy of Cd (V_Cd. The electron trap E1, found at E_c-0.178~eV, is considered to be correlated with the interstitial Cu_i⁼ in CdTe.     

Observation of interface plasmon excitation in photoemission spectroscopy from the heterostructures Cu/RbF/GaAs(100) and Cu/RbF/Ge(100)

Synchrotron radiation photoelectron spectra taken at 100 eV photon energy have been measured to characterize the interface reactions of the metal-insulator-semiconductor systems Cu/RbF/GaAs(100) and Cu/RbF/Ge(100). In comparision, similar sequences are studied on the Cu/GaAs(100) and Cu/Ge(100) interfaces without the RbF interlayer. After Cu-deposition of 1–4 Å on RbF-covered (10–14 Å) GaAs and Ge surfaces, shoulder peaks appear on both the Ga 3d and Ge 3d core levels. The shoulder peaks are shifted 1.1 and 1.4 eV to higher binding energy for the Ga 3d and Ge 3d levels, respectively. The Rb 4p and F 2p peak positions are slightly shifted between 0.25 and 0.5 eV. The broad second Ga 3d and Ge 3d peaks can be correlated to plasmon loss of electrons from these levels in a two-dimensional Rb metal-like layer formed at the Cu/RbF interface. The excitation energy of a Rb surface plasmon in a Cu-Rb-RbF system is calculated to be 1.3 eV.