P. Wisniewski

Large, nitrogen-induced increase of the electron effective mass in InyGa1−yNxAs1−x

A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys.

Determination of intervalley scattering times in GaAs from electroluminescence spectroscopy of single barrier tunneling devices

We report the results of hot electron electroluminescence (EL) experiments carried out on p-i-n GaAs/AlGaAs single barrier tunneling structures. The EL spectra show peaks arising from recombination of both ballistic and intervalley-scattered electrons with neutral acceptors in the p-type collector region. From the relative intensities of these EL features we have obtained direct spectroscopic measurements of the Γ-L and Γ-X intervalley scattering times for high energy ballistic electrons in GaAs.

Metastable and nonmetastable deep states of Ge in GaAs

We show from transport investigations that Ge doped GaAs can be either semimetallic or semiconducting depending on hydrostatic pressure and previous sample illumination. This property results from a unique crossover of two states of the Ge donor in GaAs in their energetic position under pressure. The experimental results obtained make it possible to identify the nature of these Ge‐donor states: The drastic enhancement of the electron mobility after illumination is taken as evidence of the electron transfer from the two‐electron DX− state to a neutral, localized, and unrelaxed state of the Ge donor.

Elimination of DX centerlike behavior of donors in heavily doped GaAs

The pressure dependencies of the electrical conductivity, Hall coefficient, and Shubnikov‐de‐Haas effect have been studied for n‐GaAs heavily doped with Sn and Te. The results demonstrate that the energy level related to the DX centers formed by these donors is resonant and degenerate with the conduction band of GaAs. The energy separation of the GaAs conduction‐band minimum and the DX center (EDX) for the Sn donor has been found to be similar to those of the Si‐ and S‐related DX centers (around 0.3 eV at T≊100 K), whereas EDX(Te) is much greater, at around 0.55 eV. An analysis of the sample recovery after pressure‐induced freezeout of electrons onto the DX centers has enabled the energy barrier for electron emission from the Sn‐related DX center to the conduction band and the barrier for electron capture by the DX center, the inverse process, to be determined. Both energy barriers are very small compared to those associated with Si‐ and S‐donor‐induced DX centers. The values for EDX (for Sn and Te) and t...

Unusual behaviour of the Ge DX centre in GaAs: coexistence of two localized donor states

Hall measurements have been performed as a function of hydrostatic pressure and temperature to study the effect of deep donor levels on the electron concentration and mobility in bulk GaAs heavily doped with germanium. For the first time, the coexistence of the metastable DX centre and the nonmetastable localized deep A1 level has been unambiguously observed in GaAs. Furthermore, the authors have determined the energy positions and pressure dependences of both resonant levels (0.066 eV and -6.9 meV kbar-1 for the A1 level and 0.105 eV and -10 meV kbar-1 for the DX centre) and the energy barrier for electron emission from the DX centre (0.285 eV). The latter appeared to be pressure independent. From the mobility behaviour during depopulation of DX centres, an elegant proof for the negative-U character of DX centres and the positive-U character of deep A1 levels has been obtained.

Magnetotransport in high mobility InSbCdTe heterojunctions: Electric spin-splitting of subbands and high pressure effects

Abstract Magneto-transport measurements are reported on the high-mobility, low-carrier-density (μ = 16 000 − 22 000 cm2V−1s−1 and Ns = 1.8 − 4.2 × 1011 cm−2), two dimensional electron gas in InSbCdTe heterojunctions, realised as a result of improvements in growth techniques. Measurements carried out at hydrostatic pressures up to 10 kbar show that Ns decreases with increasing pressure, suggesting that the electrons in the 2DEG originate from a band of interface states ∼ 100 meV above the InSb conduction band edge at the InSbCdTe interface. The temperature dependence of the Hall effect suggests that the persistent photoconductivity observed in InSbCdTe heterojunctions is due to charge separation in InSb. The low-field magnetoresistance of the heterojunctions is at first positive and then negative due to the presence of a spin-splitting of the subbands of around 3 meV at the Fermi energy, present even in zero applied magnetic field, and the experimental results aer compared with self-consistent calculations of this effect.

High pressure studies of electron mobility in heavily doped GaAs: fitting of the absolute value

The mobility, mu , and the carrier concentration, n, of GaAs heavily doped with Si, Sn, and Te is measured at pressures up to 20 kbar and at temperatures from 4.2 to 295 K. The samples of GaAs:Si and GaAs:Sn exhibit strong changes of n and mu with pressure. For these samples a theoretical fit is presented to the absolute values of mu , including scattering mechanisms caused by spatially correlated charged donors, short-range potentials related to DX centres and compensating ionized acceptors. The suggestion that after applying pressure the main influence on mu behaviour originates from spatially correlated charged donors is confirmed. The energy position of the Te-related DX level appears to be much higher than that for Si- and Sn-related DX centres.