R. Alabedra

An Hg 0.3 Cd 0.7 Te avalanche photodiode for optical-fiber transmission systems at λ = 1.3 µm

The purpose of this paper is the characterization of Hg<inf>0.3</inf>Cd<inf>0.7</inf>Te avalanche photodiodes at γ = 1.3 µm. These devices are manufactured by tile Société Anonyme des Télécommunications. The multiplication noise for these APDs is measured. The value of the ratio<tex>k</tex>= β/α is deduced from noise measurements, β and α being, respectively, the hole and electron ionization coefficients. It is shown that these HgCdTe APDs are promising candidates for detectors of 1.3-µm optical communication.

Low-frequency FM-noise-induced lineshape: a theoretical and experimental approach

Linewidth determination by self-heterodyne or self-homodyne methods may lead to mistaken interpretation, because these measurements often include significant broadening due to low-frequency FM noise. The effects of FM noise on these linewidth measurement schemes are investigated. An analytical formulation of the photocurrent autocorrelation function is given for different frequency noise signatures, the lineshape being extracted from numerical implementation. We apply these results to linewidth prediction for 850-nm commercial vertical-cavity surface-emitting lasers and get almost perfect agreement between the theoretical and the experimental approaches.

Hg/sub 0.4/Cd/sub 0.6/Te 1.55- mu m avalanche photodiode noise analysis in the vicinity of resonant impact ionization connected with the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg/sub 1-x/Cd/sub x/Te avalanche photodiodes manufactured using planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55- mu m detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio beta / alpha (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Delta /E/sub g/ where Delta is the spin-orbit splitting energy and E/sub g/ is the bandgap energy. It turns out that in these alloys around x=0.6, Delta is very close to the bandgap energy so beta / alpha reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg/sub 1-x/Cd/sub x/Te is a good candidate for 1.3- mu m to 1.6- mu m avalanche photodiodes. >

Impact ionization resonance and auger recombination in Hg 1 - x Cd x Te ( 0.6 &#8804; x &#8804; 0.7 )

The purpose of this paper is the study of the impact ionization and the Auger recombination in Hg 1-x Cd x Te avalanche photodiodes, with 0.6 \leq x \leq 0.7 . For x \sim 0.7 it is shown that the spin orbit splitting Δ is lower than the bandgap energy E g so that impact ionization is initiated by holes from the Split-off valence band. For x \sim 0.6, \Delta \sim E_{g} , the rate of the Auger recombination is maximum, corresponding to a resonant impact ionization and to a maximum ratio k = \beta / \alpha where α and β are, respectively, the impact ionization coefficient for electrons and holes.

Hg/sub 0.56/ Cd/sub 0.44/ Te 1.6- to 2.5- mu m avalanche photodiode and noise study far from resonant impact ionization

An investigation was made on the avalanche multiplication and impact ionization processes in p-n/sup -/-n/sup +/ junctions formed in Hg/sub 0.56/Cd/sub 0.44/Te solid solutions. Photocurrent multiplication was determined at 300 K in planar p-n/sup -/-n/sup +/ structures characterized by a breakdown voltage of 30 V. The experimental results were used to calculate the electron, alpha , and hole, beta , ionization coefficients. It was found that alpha is greater than beta because Delta , the spin-orbit splitting energy, is higher than the bandgap energy. These experimental results were in satisfactory agreement with multiplication noise measurements using separate electron and hole injection. >

Impact ionization rates for electrons and holes in Hg0.3Cd0.7Te in avalanche photodiodes for optical fiber transmission systems at λ = 1.3 μm

In this paper preliminary experimental results are shown on Hg0.3Cd0.7Te avalanche photodiodes with x = 0.70 and Eg = 0.84 eV. In the first part, both multiplication coefficients Mp and Mn,p are determined. The ionization coefficients α and β for electrons and holes are calculated. The ionization coefficient ratio, k = β/α, is deduced and is about 10. In the second part, noise characterization will be presented. The excess noise F(M), given by McIntyres theory, confirms that k is about 10.

Correlation between tuning section electrical noise and optical amplitude fluctuations in DBR two- and three-section tunable lasers emitting around 1.55 μm

Most common monomode tunable laser diodes use carriers injection to change a bulky semi-conductor materials optical index (through absorption), with the aim of switching the emission wavelength, thanks to the phasis comb spectrum or Bragg filtering evolution. This index change existe in the active, phase and Bragg section. Independently, current injection in a laser diode involves the existance of a fundamental shot noise and of excess 1/f noise. This noise power creates optical index fluctuations in all of the 3 sections, and so modulates the lasers light field. As there is a close link between absorption and refraction index in semiconductors, through Kramers-Kronig relationships this modulation has an influence on both phase and amplitude of the laser field. The aim of this paper is to establish the correlations existing between electrical shot noise and 1/f noise of the tuning sections and the laser fields optical noise.

Frequency noise in 850-nm oxidized VCSELs

The spectral purity of laser radiation is a key point in the performance of coherent optical network. As 850nm VCSELs are being used in short distance interconnections, the evaluation of the frequency noise level is essential. Using a Fabry-Perot cavity as a frequency discriminator, the frequency noise spectrum is being investigated in the medium frequency and high frequency range (up to 1GHz). Frequency noise spectra show a 1/fn part in the medium frequency domain and a traditional white noise part in the high frequency domain. The aim of this paper is to present our measurements concerning 850nm-selectively-oxidized VCSELs and to investigate the different factors which have a quantitative influence on the frequency noise spectrum.

Valence band structure of Cd0.7Hg0.3Te determined by angular resolved photoemission

We have performed angular resolved photoemission at hv = 21.2 eV on cleaved CdHgTe(110) surfaces using a fast spectrometer. Image processing of the EDC curves has permitted us to draw the three upper valence bands, i.e. the heavy holes band, the light hole band and the split-off band. Measurement of the slope of the split-off band has given the constant p used in the k . p band calculation method. By fitting the k . p method to the experimental band dispersion, we have determined the effective mass of the holes in the whole Brillouin zone.

Détermination du facteur de multiplication M pour un fonctionnement optimal des photodétecteurs à avalanche

AnalyseCet article traite de la détermination du facteur de multiplication Mpour un fonctionnement optimal des photodétecteurs à avalanche compte tenu du bruit du montage électronique. On compare deux types de photodétecteur à avalanche: une structure au silicium n+ πpπp+et une hétérostructure du typs GaAlAs. Dans le calcul de la Puissance Equivalente de Bruit (peb)du montage, on utilise la relation Si(f) =2 IphoMxdans laquelle le paramètre x est déterminé expérimentalement. L’exposant x compris entre 2 et 4 est déterminant dans l’expression dupebdont la valeur idéale pour un systéms de photodétecteur à avalanche est obtenue quand x est égal à 2.AbstractThe purpose of this paper is relative to the determination of the multiplication factor Mfor an optimum behaviour of the avalanche photodetector. Two types of avalanche photodetector s are compared: a silicon structuren+ πpπp+Read diode and a GaAlAs heterostructure. Calculating the Noise Equivalent Power (nep)of the whole system, the law Si(f) =2q IphoMxis used, where the parameter x is determined experimentally in both avalanche photodetectors. The exponent x (between 2 and 4) dominates in thenepexpression and the idealnepfor the avalanche photodetector system is obtained when x equals 2.