Low avalanche noise characteristics in thin InP p+-i-n+ diodes with electron initiated multiplication

We have performed electron initiated avalanche noise measurements on a range of homojunction InP p⁺-i-n⁺ diodes with “i” region widths, w ranging from 2.40 to 0.24 μm. In contrast to McIntyre's noise model a significant reduction in the excess noise factor is observed with decreasing w at a constant multiplication in spite of α, the electron ionization coefficient being less than β, the hole ionization coefficient. In the w=0.24 μm structure an effective β/α ratio of approximately 0.4 is deduced from the excess noise factor even when electrons initiate multiplication, suggesting that hole initiated multiplication is not always necessary for the lowest avalanche noise in InP-based avalanche photodiodes     

Avalanche multiplication noise characteristics in thin GaAs p+-i-n+ diodes

Avalanche noise measurements have been performed on a range of homojunction GaAs p⁺-i-n⁺ and n⁺-i-p ⁺ diodes with “i” region widths, ω from 2.61 to 0.05 μm. The results show that for ω⩽1 μm the dependence of excess noise factor F on multiplication does not follow the well-established continuous noise theory of McIntyre [1966]. Instead, a decreasing noise factor is observed as ω decreases for a constant multiplication. This reduction in F occurs for both electron and hole initiated multiplication in the thinner ω structures even though the ionization coefficient ratio is close to unity. The dead-space, the minimum distance a carrier must travel to gain the ionization threshold energy, becomes increasingly important in these thinner structures and largely accounts for the reduction in noise     

Low multiplication noise thin Al0.6Ga0.4Asavalanche photodiodes

Avalanche multiplication and excess noise were measured on a series of Al_0.6Ga_0.4As p⁺in⁺ and n⁺ip⁺ diodes, with avalanche region thickness, w ranging from 0.026 μm to 0.85 μm. The results show that the ionization coefficient for electrons is slightly higher than for holes in thick, bulk material. At fixed multiplication values the excess noise factor was found to decrease with decreasing w, irrespective of injected carrier type. Owing to the wide Al_0.6Ga_0.4As bandgap extremely thin devices can sustain very high electric fields, giving rise to very low excess noise factors, of around F~3.3 at a multiplication factor of M~15.5 in the structure with w=0.026 μm. This is the lowest reported excess noise at this value of multiplication for devices grown on GaAs substrates. Recursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is used to model the nonlocal nature of impact ionization giving rise to the reduction in excess noise with decreasing w. Although the hard threshold dead space model could reproduce qualitatively the experimental results, better agreement was obtained from the history-dependent model     

The hydrogenated amorphous silicon reach-through avalanchephotodiodes (a-Si:H RAPDs)

The RAPD (reach-through avalanche photodiode) structure is adopted to improve the electrical and optical performance of photosensing devices made of a-Si:H. Both the electron-injection n⁺ -i-δp-i-p⁺ and hole-injection p⁺-i-δn-i-n⁺ a-Si:H RAPDs are fabricated on the indium-tin-oxide-coated glass substrates by plasma-enhanced chemical vapor deposition (PECVD). The photocurrent multiplication method is employed to study the multiplication factors and the impact ionization coefficients of the RAPDs. Since the electron-injection models have better performance, the relationships between the device dimensions and characteristics, such as I-V curves, optical gains, impact ionization rates, and excess noise factors, are further studied. The results indicate that the a-Si:H RAPD is a promising device for photosensing applications     

Improved germanium avalanche photodiodes

New kinds of germanium avalanche photodiodes with n+-n-p and p+-n structures were devised for improved excess noise and high quantum efficiency performance. Multiplication noise, quantum efficiency, and pulse response were studied and compared with those of the conventional n+-p structure diode. Multiplication noise of the new type of diodes were measured in the wavelength range between 0.63 and 1.52 μm. The effective ionization coefficient ratio of the p+-n diode was lower than unity at a wavelength longer than 1.1 μm and 0.6-0.7 at 1.52 μm, and that of the n+-n-p diode was 0.6-0.7 in the whole sensitive wavelength region. Response times were evaluated by using a mode-locked Nd:YAG laser beam and a frequency bandwidth wider than 1 GHz was estimated. Receiving optical power levels were compared with each other using parameters measured in this study.     

Ionization coefficient measurement in GaAs by using multiplication noise characteristics

Multiplication noise measurements for p⁺n type (100) GaAs avalanche photodiodes with various n-layer dopings ranging from 6 × 10¹⁵ to 9 × 10¹⁶ cm^?3 confirmed that the ionization coefficient of electrons α is about two times larger than that of holes β in the electric field range from 2.4 × 10⁵ to 5.6 × 10⁵ V/cm. When pure electrons were injected into the avalanche region, the multiplication noise power was proportional to the 2.7th power of the multiplication factor and the ionization coefficient ratio $\text{k =}\text{β}\text{α}$ was constant, where k = 0.5 in the above electric field range. The result was consistent with the multiplication factor dependence on light wavelength. Using the constant ionization coefficient ratio k and the multiplication factor dependence on applied bias voltage, ionization coefficients α and β for electrons and holes were estimated.     

Hg0.56 Cd0.44 Te 1.6- to 2.5-μm avalanchephotodiode and noise study far from resonant impact ionization

An investigation was made on the avalanche multiplication and impact ionization processes in p-n^--n⁺ junctions formed in Hg_0.56Cd_0.44Te solid solutions. Photocurrent multiplication was determined at 300 K in planar p-n^- -n⁺ structures characterized by a breakdown voltage of 30 V. The experimental results were used to calculate the electron, α, and hole, β, ionization coefficients. It was found that α is greater than β because Δ, 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     

Avalanche Multiplication in InAlAs

A systematic study of avalanche multiplication on a series of In _0.52Al_0.48As p⁺-i-n⁺ and n ⁺-i-p⁺ diodes with nominal intrinsic region thicknesses ranging from 0.1 to 2.5 mum has been used to deduce effective ionization coefficients between 220 and 980 kVmiddotcm^-1. The electron and hole ionization coefficient ratio varies from 32.6 to 1.2 with increasing field. Tunneling begins to dominate the bulk current prior to avalanche breakdown in the 0.1-mum-thick structure, imposing an upper limit to the operating field. While the local model can accurately predict the breakdown in the diodes, multiplication is overestimated at low fields. The effects of ionization dead space, which becomes more significant as the intrinsic region thickness reduces, can be corrected for by using a simple correction technique     

Extremely Low Excess Noise in InAs Electron Avalanche Photodiodes

Measurements of the avalanche multiplication noise in InAs p-i-n and n-i-p diodes at room temperature demonstrate unambiguously that the avalanche multiplication process is dominated by impact ionization of electrons. This results in the excess noise factor for electron initiated multiplication asymptotically approaching a maximum value just less than two and becoming virtually gain-independent for higher gains. Measurements for predominantly hole initiated multiplication show corresponding high excess noise factors suggesting the electron to hole ionization coefficient ratios are comparable to those reported for $hbox{Hg}_{1-{x}}hbox{Cd}_{x}hbox{Te}$ electron avalanche photodiodes.      

An Hg0.3Cd0.7Te avalanche photodiode for optical-fiber transmission systems at λ = 1.3 µm

The purpose of this paper is the characterization of Hg0.3Cd0.7Te avalanche photodiodes at γ = 1.3 µm. These devices are manufactured by tile Société Anonyme des Télécommunications. The multiplication noise for these APD's is measured. The value of the ratiok= β/α is deduced from noise measurements, β and α being, respectively, the hole and electron ionization coefficients. It is shown that these HgCdTe APD's are promising candidates for detectors of 1.3-µm optical communication.     

Comparison of available detectors for digital optical fiber systems for the 1.2-1.55 µm wavelength range

Receiver sensitivity is estimated at 1.3 and 1.5 μm for commercial Ge APD's for bit rates between 8 and 1200 MBd, for a variety of APD diameters and operating temperatures. Although both holes and electrons are injected into the depletion region at these wavelengths, the measured photocurrent excess multiplication noise is found empirically to be well described by the simple expression for unilateral carrier injection into the depletion region, while the measured noise on the bulk leakage current can be characterized by the photocurrent parameters for wavelengthssim1.8 mum. Measurements at BTRL on a 140 Mbit/s system receiver using an Optitron GA-1 Ge APD at temperatures in the range20-60degC agree within 1 dB with the theoretical model using these data. The performance of Ge APD-based receivers is strongly influenced by noise on the leakage current and is therefore susceptible to temperature fluctuations. The ionization rates for holes and electrons are comparable in Ge, resulting in a high excess noise factor and a strong dependence of multiplication factor on bias voltage. Thus, APD's for long-wavelength digital optical receivers operating below ∼1 GBd require a bulk leakage current densityll 10^{-4}A/cm²and markedly different ionization rates for holes and electrons, in order to match the otherwise superior performance of the present-day high-impedance p-i-n/FET hybrid.     

Dark-current multiplication noises in avalanche photodiodes and optimum gains

Theoretical probabilities for a number of hole-electron pairs are derived for the dark-current and signal multiplication noises in avalanche photodiodes (APD). The excess noise factors for the dark-current multiplication noises are given in forms similar to the signal multiplication noise. The error probabilities influenced by the multiplication noises are calculated, and it is pointed out that the error probabilities basically have no dependency on the ratio of the ionization coefficientskwhen APD has no dark-current source. The optimum gain characteristics are analyzed for the detection systems which include the multiplication noises, the thermal noise of load resistance, and the following amplifier's noise.     

A Monte Carlo investigation of multiplication noise in thin p+-i-n+ GaAs avalanche photodiodes

A Monte Carlo (MC) model has been used to estimate the excess noise factor in thin p⁺-i-n⁺ GaAs avalanche photodiodes (APD's). Multiplication initiated both by pure electron and hole injection is studied for different lengths of multiplication region and for a range of electric fields. In each ease a reduction in excess noise factor is observed as the multiplication length decreases, in good agreement with recent experimental measurements. This low noise behavior results from the higher operating electric field needed in short devices, which causes the probability distribution function for both electron and hole ionization path lengths to change from the conventionally assumed exponential shape and to exhibit a strong dead space effect. In turn this reduces the probability of higher order ionization events and narrows the probability distribution for multiplication. In addition, our simulations suggest that fur a given overall multiplication, electron initiated multiplication in short devices has inherently reduced noise, despite the higher feedback from hole ionization, compared to long devices     

Excess Avalanche Noise in In0.52Al0.48As

Avalanche multiplication and excess noise arising from both electron and hole injection have been measured on a series of In_0.52Al_0.48As p⁺-i-n⁺ and n ⁺-i-p⁺ diodes with nominal avalanche region widths between 0.1 and 2.5 mum. With pure electron injection, low excess noise was measured at values corresponding to effective k=beta/alpha between 0.15 and 0.25 for all widths. Enabled ionization coefficients were deduced using a non-local ionization model utilizing recurrence equation techniques covering an electric field range from approximately 200 kV/cm to 1 MV/cm     

Responsivity and impact ionization coefficients ofSi1-xGex photodiodes

The spectral response and impact ionization coefficient ratio of Si_1-xGe_x have been determined. Measurements were made on p⁺-i-n⁺ diodes grown by solid/gas source molecular beam epitaxy. The diodes are characterized by reverse breakdown voltages of 4-12 V and dark currents of 20-170 pA/μm² . The long wavelength cut-off of the diodes increases from 1.2 μm to 1.6 μm as x increases from 0.08 to 1.0 with a maximum responsivity of 0.5 A/W in all the diodes tested. The ratio α/β varies from 3.3 to 0.3 in the same composition range, with α/β=1 at x≅0.45. These results have important implications in the use of this material system in various photodetection applications     

Excess noise design of InP/GaInAsP/GaInAs avalanche photodiodes

An InP/GaInAsP/GaInAs avalanche photodiode (APD) with separate absorption and multiplication (SAM) regions has been designed taking into account the excess noise generated in GaInAsP and GaInAs. The multiplication factor dependence of the excess noise factorFhas been calculated using realistic electron and hole ionization rates in InP, GaInAsP, and GaInAs, assuming that the avalanche multiplication occurs not only in InP but in GaInAsP and GaInAs. The calculatedFvalues have been compared to the experimental ones measured on a planar-type InP/GaInAsP/GaInAs APD for illumination at a wavelength of 1.3 μm. It has been found the the calculated excess noise agrees very well with the experimental measurements. The limited ranges of device parameters in which the conditions of minimal excess noise, tunneling current, and charge pile-up are satisfied have been obtained. We conclude that the excess noise generated in GaInAsP and GaInAs should be considered in a practical device design.     

Hg0.4Cd0.6Te 1.55-μm avalanche photodiodenoise analysis in the vicinity of resonant impact ionization connectedwith the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg_1-xCd_xTe 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-μm detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio β/α (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Δ/E_g where Δ is the spin-orbit splitting energy and E _g is the bandgap energy. It turns out that in these alloys around x=0.6, Δ is very close to the bandgap energy so β/α reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg_1-xCd_xTe is a good candidate for 1.3-μm to 1.6-μm avalanche photodiodes     

Avalanche multiplication characteristics ofAl0.8Ga0.2As diodes

The avalanche multiplication characteristics of Al_0.8Ga _0.2As have been investigated in a series of p-i-n and n-i-p diodes with i-region widths, w, varying from 1 μm to 0.025 μm. The electron ionization coefficient, α, is found to be consistently higher than the hole ionization coefficient, β, over the entire range of electric fields investigated. By contrast with Al_xGa _1-xAs (x⩽0.6) a significant difference between the electron and hole initiated multiplication characteristics of very thin Al_0.8Ga_0.2As diodes (w=0.025 μm) was observed. Dead space effects in the diodes with w⩽0.1 μm were found to reduce the multiplication at low bias below the values predicted from bulk ionization coefficients. Effective α and β that are independent of w have been deduced from measurements and are able to reproduce accurately the multiplication characteristics of diodes with w⩾0.1 μm and breakdown voltages of all diodes with good accuracy. By performing a simple correction for the dead space, the multiplication characteristics of even thinner diodes were also predicted with reasonable accuracy     

Impact ionization characteristics of III-V semiconductors for awide range of multiplication region thicknesses

Recently, an impact ionization model, which takes the nonlocal nature of the impact ionization process into account, has been described. This model incorporates history-dependent ionization coefficients. Excellent fits to experimental gain and noise measurements for GaAs were achieved using an effective field approach and simple analytical expressions for the ionization probabilities. In the paper, we briefly review the history-dependent model and apply it to Al_0.2 Ga_0.8As, In_0.52Al_0.48As and InP avalanche photodiodes. For the study, the gain and noise characteristics of a series of homojunction avalanche photodiodes with different multiplication thicknesses were measured and fit with the history-dependent model. A “size-effect” in thin (<0.5 μm) multiplication regions, which is not adequately characterized by the local-field avalanche theory, was observed for each of these materials. The history-dependent model, on the other hand, achieved close agreement with the experimental results     

H2+和D2+谐波强度与波长的关系

为了了解H₂+及其同位素分子谐波光谱效率与激光波长之间的关系,采用求解2维薛定谔方程的方法,理论研究了600nm~1600nm激光波长下H₂+和D₂+谐波光谱强度随波长的变化关系。结果表明,光谱强度随波长增大而减小;在短波长区间,H₂+光谱强度减小的倍率要大于D₂+,在长波长区间,H₂+光谱强度减小的倍率要小于D₂+;此外,在弱光强下,H₂+光谱强度总是大于D₂+, 在强光强下,H₂+光谱强度在短波长区间小于D₂+, 而其在长波长区间大于D₂+; 核间距延伸和电荷共振增强电离在H₂+和D₂+谐波光谱强度变化上起到主要作用。这一结果对分子谐波调控是有帮助的。