M. Pérotin

Liquid‐phase‐epitaxial growth of Ga0.96Al0.04Sb: Electrical and photoelectrical characterizations

Ga0.96Al0.04Sb layers have been grown by liquid‐phase epitaxy on GaSb substrates at 400, 450, and 550 °C. The 450 °C growth leads to the best control of the layer’s quality. At 450 °C the natural p‐type doping of the layers is limited by the thermal acceptors ( p∼4×1016 cm−3) and the lowest reproducible uniform electron concentration obtained by Te compensation is n∼1016 cm−3. Electrical and photoelectrical properties of Schottky diodes and mesa Zn‐diffused homojunctions realized on these layers are described. They are strongly affected by surface effects attributed to the band bending of n‐type GaAlSb. Some parameters can be deduced from the various characterizations: the carrier lifetime in the space‐charge region of Zn‐diffused p+/n junctions, τ∼3×10−10 s; electron diffusion lengths in the as‐grown Ga0.96Al0.04Sb layer, Ln=5 μm, and in the Zn‐diffused layer, Ln=1.5 μm; and the hole diffusion length in the n‐compensated layers, Lp=1 μm.

Photoelectric properties of GaSb Schottky diodes

Electrical and photoelectrical properties of GaSb Schottky diodes obtained by evaporating gold metal dots on sulphur treated or chemically etched surfaces of Te-doped n-GaSb crystals (grown from melt by Czochralski method), with Hall carrier density in the range of 1.8–6.5×1017 cm−3, were studied. J/V characteristics with an ideality factor ranging between 1.17 and 1.22 were measured on Schottky diodes prepared on sulphur passivated surfaces. After image force effect correction, photoelectric determination of the barrier height (qΦb=0.598±0.006 eV) has been found to be independent of the surface treatment and, in the case of the sulphur-treated diodes, in good agreement with the value obtained through C−2 vs reverse bias measurements (qΦb=0.6±0.01 eV). Through spectral response analysis of Schottky diodes, an estimation of minority carrier diffusion length value is given. A major role of sulphur passivation on preparation of Schottky barrier with good and well reproducible electrical properties is confirmed.

Improvement of dark current of Ga(A1)Sb mesa diodes using (NH4)2S treatment

Abstract The effects of chemical sulphuration on GaSb mesa photodiodes performance were investigated by electrical characterization. (NH 4 ) 2 S treatment was found to be very effective in reducing the reverse dark currents by one module value, leading them down to I = 0.2 μ A (V = 1 V) for a φ = 60μ m diameter diode. The capacitance variation versus frequency, investigated from 10 kHz to 1 MHz, becomes flat over the whole range of frequency, attesting of a volume conduction mechanism. These performances exhibited a remarkable stability during 1 year, without encapsulation. The X-ray photoelectron spectrum of the Sb 3d level shows that after (NH 4 ) 2 S treatment the surface is free of native Sb oxides, Sb-.sbnd;S bonds being created by the adsorption of sulphur atoms on the surface These surface modifications are responsible for the observed improvement in characteristics and their stability.

Calculation of Alloy Disorder Influence on Hole Ionization Behavior in Ga1-xAlxSb Compounds

The calculation of the ionization probability and of the ionization coefficients of the holes of the spin split-off valence band in Ga1-x Alx Sb has been made for various compositions 0<x<0.08. This range allows us to obtain the situations in which the ratio of spin orbit splitting Δ to the energy gap E g decreases from 1.05 to 0.89. It is shown that if the alloy disorder is neglected, the hole ionization coefficient k p exhibits a continuous variation with Δ/E g (or x); if not, k p is strongly increased and shows a maximum for x=0.02 in the composition range in which Δ≥E g (Δ/E g=1.006). The comparison with experimental results is presented and allows an estimation of the mean free path of the holes; the strong influence of this parameter on the k p values is discussed.

NEAR-INFRARED ELECTROABSORPTION IN P+/N-/N+ GASB DIODES

Liquid phase epitaxial growth of Te‐compensated GaSb results in a very low doped n− GaSb epilayer (n≊1015 cm−3). Be+‐implanted photodiodes produced from this material exhibit voltage breakdown values reaching 70 V. Generation‐recombination lifetimes in the space charge region around 10−8 s have been deduced from these diode photoelectrical properties. The high value of the space charge width leads to an efficient redshift due to the electroabsorption. The variation of the absorption coefficient value is 1350 cm−1 at 1.72 μm for a variation of the electric field maximum of 1.2×105 V/cm.

Incidence of Final States-Density for Impact Ionization on the Electron Ionization Rate

The anisotropy of electron impact ionization rate as related to the band structure is experimentally established. At present, theoretical studies often attribute its dependence to the overlap integrals variations, alloy disorder effect or impact ionization process involving a second conduction band. We present a different numerical calculation of electron impact ionization probability in Ga1-xAlxSb avalanche photodiodes (0≤x≤0.08). The ionization probability is calculated directly from the numerical evaluation of the matrix element including the full details of the first conduction band. It is found that the dependence of the electron ionization probability on the final states-density for impact ionization is very crucial compared with variations in overlap integrals or alloy disorder effect.

Be+ implanted GaInAsSb/GaSb photodiodes

Abstract Be + implantation technology has been applied to realize p + /n − junctions in quaternary GaInAsSb n − alloys grown on GaSb substrates by liquid phase epitaxy. 2 μm cut-off mesa homojunctions have been prepared and characterized: the external quantum efficiency measured without any antireflecting coating reaches η ext = 0.5 at 1.8 μm. Room temperature dark reverse current densities J rev (300K) = 1–5 mA cm −2 measured at V = −0.5 V are 10–100 times lower than those usually measured in GalnAsSb photodetectors; at low reverse polarization voltage the rapid decrease in the current levels as a function of the temperature leads to a strong increase in the performances of the photodiodes using simple Peltier cooling (J rev (220 K) = 12 μA cm −2 at V = − 0.2 V). In the forward direction the behaviour of the dark currents as a function of the temperature leads us to conclude that diffusion is the dominant mechanism in these photodiodes in the range 320−220 K.

Be+ ion implantation in Ga(Al)Sb layers: radiation damage

Abstract Be + ion implantation into Te-doped Ga(Al)Sb ( x Al ≈ 4% ) epilayers was performed to realize the p + layer of a p + /n − GaAlSb/GaSb n + IR avalanche photodetector. A double implantation using 100+50 keV energies and fluences around 10 13 cm −2 is found to be a convenient procedure to produce a junction depth of 0.5 μm. Damage levels created by Be + ions in GaAlSb layers are simulated and investigated through channelling measurements and it is seen that heat treatments (15 min, 450 °C, H 2 ) improve the activation. This paper clearly shows that Be + ion implantation leads to a low damage level in this III–V compound.

Dependence of impact ionization coefficients on electric‐field profile and injection mode approximations

The validity of the determination of the ionization coefficients deduced from the experimental measurement of photocurrent multiplication Mph in GaAlSb diodes, in which the electric‐field profile is nonlinear and successive pure hole and pure electron injections cannot be made, are compared and discussed. Three methods for determining ionization coefficients kp and kn are discussed: (i) adjusting kp and kn in order to fit the experimentally observed Mph values using an approximated linear electric field; (ii) the same method applied to a more realistic electric‐field profile; (iii) the Grant method in which kp and kn are calculated from the results of multiplication measurements in the case of pure injections and using this last electric‐field profile. It is concluded that when the condition of pure injection is not fulfilled the Grant method may lead to erroneous k values and the adjustment method is more valid.

Evaluated Performances Of Ga0.96Al0.04Sb Avalanche Photodetectors

This paper presents an evaluation of the noise equivalent power (NEP) of 1.55 pm avalanche photodetectors based on Ga0.96 Al0.04 Sb, liquid phase epitaxy (LPE) grown junctions. Deduced from some measured photoelectrical parameters and from others publicated ones an optimum NEP of 3.5 x 10 -12 W/ √Hz is calculated for a doping level of 3 x 10 21 m-3.