Undopedn-Type GaSb Grown by Liquid Phase Epitaxy

Abstract

In this paper we investigate the effect of stochasticity in the spatial and temporal distribution of supernova remnants on the spectrum and chemical composition of cosmic rays observed at Earth. The calculations are carried out for different choices of the diffusion coefficient D(E) experienced by cosmic rays during propagation in the Galaxy. In particular, at high energies we assume that D(E) ∝ E δ , with δ = 1/3 and δ = 0.6 being the reference scenarios. The large scale distribution of supernova remnants in the Galaxy is modeled following the distribution of pulsars, with and without accounting for the spiral structure of the Galaxy. We find that the stochastic fluctuations induced by the spatial and temporal distribution of supernovae, together with the effect of spallation of nuclei, lead to mild but sensible violations of the simple, leaky-box-inspired rule that the spectrum observed at Earth is N (E) ∝ E −α with α = γ + δ, where γ is the slope of the cosmic ray injection spectrum at the sources. Spallation of nuclei, even with the small rates appropriate for He, may account for small differences in spectral slopes between different nuclei, possibly providing an explanation for the recent CREAM observations. For δ = 1/3 we find that the slope of the proton and helium spectra are ∼ 2.67 and ∼ 2.6 respectively (with fluctuations depending on the realization of source distribution) at energies around ∼ 1 TeV (to be compared with the measured values of 2.66 ± 0.02 and 2.58 ± 0.02). For δ = 0.6 the hardening of the He spectra is not observed. The stochastic effects discussed above cannot be found in ordinary propagation calculations, such as GALPROP, where these effects and the point like nature of the sources are not taken into account. We also comment on the effect of time dependence of the escape of cosmic rays from supernova remnants, and of a possible clustering of the sources in superbubbles. In a second paper we will discuss the implications of these different scenarios for the anisotropy of cosmic rays.

The physics and technology of gallium antimonide: An emerging optoelectronic material

“…88,92,93 Capasso and co-workers 88 could achieve very low net donor concentration in the range of 10 14 -10 15 cm Ϫ3 from undoped Ga-rich solutions in the 300-375°C range and by Te compensation using Ga-rich melt at 500°C. Miki and co-workers 94 were also able to grow undoped n-type layers at 400°C from Ga-rich melt with net donor concentration of ϳ10 15 cm Ϫ3 and mobility as high as 7700 cm 2 /V s. In our studies we have observed that undoped layers grown from antimony-rich melts always exhibit p-type conductivity irrespective of the growth temperature. 96 In contrast, a type conversion from p to n was observed in layers grown from Ga-rich melts below 400°C.…”

“…There exist quite a few reports on growth of GaSb by LPE technique. [87][88][89][90][91][92][93][94][95][96] Ga-, Sb-, Sn-and Bi-rich melts have been used for the growth in the temperature range of 330-680°C. By carrying out growth at low temperatures, the native acceptor concentration could be reduced to a level of 10 16 cm Ϫ3 .…”

High-resistivity GaSb bulk crystals grown by the vertical bridgman method

“…15 ρ ϭ * ρ ϭ * µ ϭ * µ ϭ * LPE; undoped GaSb grown on undoped GaSb at P ϭ 1.1 ϫ 10 16 P ϭ * 445°C (p-type ) and 400°C (n-type), Ref. 16 N ϭ 3.8 ϫ 10 15 ρ ϭ * ρ ϭ * µ ϭ * µ p ϭ 620; µ n ϭ 7,700 Molecular beam epitaxy (MBE); Undoped GaSb P ϭ 3 ϫ 10 12 P ϭ * on GaSb or on semi-insulating GaAs substrates at ρ ϭ * ρ ϭ * 600-630°C, Ref. 17 µ ϭ 500 µ ϭ * MBE; Te-doped GaSb on (311)B GaSb, Ref.…”

“…Numerous attempts have been made to reduce the native defect content by growing the crystals under varying conditions. 7,[11][12][13][14][15][16][17][18][19][20] Table I summarizes some of the key parameters that resulted in lower carrier concentration or higher resistivity in GaSb. In this paper, we report the electrical properties of tellurium (Te)-compensated, GaSb bulk crystals of 50-mm diameter (2-in.…”

Magnetic Impurities in Gallium Antimonide

“…Recently much attention has been focused on GaSb and heterostructures based on Sb narrow-gap semiconducting compounds due to their applicability in opto-electronic devices, such as lasers and photodetectors for near and mid-infrared region [1 to 3]. The growth of GaSb layers of semiconductor quality has been achieved by different techniques: liquid phase epitaxy [4], metal-organic chemical vapor deposition (MOCVD) [5], and molecular beam epitaxy [6,7]. The review of basic results and device related characteristics has been published in [1].…”