InP Diodes Research Articles

Detection of junction failures and other defects in silicon and III–v devices using the LBIC technique in lateral configuration

A scanning light microscope was used to obtain light beam induced current (LBIC) profiles in samples containing a p-n junction either parallel or perpendicular to the surface scanned by the beam. Using this technique we studied the quality of the junction of InP(n)-InP(p) diodes, which are one of the intermediate structures obtained during the processing of InGaAsP/InP lasers. The same technique was successfully employed also for the quality control of silicon power diodes. It was thus demonstrated that the LBIC technique, operated in the standard and in the lateral configuration at a resolution better than 10 μm, is a powerful, nondestructive tool which can be efficiently used for the quantitative measure of the damage present at any kind of diode junctions.

A double metal structure Pt/Al/n-InP diode

A high performance double metal structure, Pt/Al/n-InP diode is discussed. The diode exhibits an effective barrier height of 0.74 eV, forward characteristics with an ideality factor n=1.11 over five decades, and a reverse leakage current of 1.34×10−4 A/cm2 at −3 V. A detailed study of the electrical characteristics and secondary ion mass spectroscopy analysis of the sample suggest that the high barrier height is due to formation of an interfacial layer at the contact interface. The diode exhibits good thermal stability, maintaining a barrier height of 0.70 eV after annealing at 300 °C for 10 h.

Electron trapping in thin oxide on GaAs and InP at 77 K

Electron trapping in thin anodized layers on GaAs and InP at 77 K was studied using the flat band voltage shift method. Compared with the trap characteristics at room temperature, the capture cross section and density were increased. The trap sites with very small capture cross section at room temperature were not detected at 77 K. A few trap sites were detected at 77 K which possibly act as shallow levels at room temperature. For both GaAs and InP diodes, trap characteristics were found to be a function of the processing conditions.

MIS diodes on n-InP with tantalum oxide interfacial layer grown by rapid thermal oxidation of tantalum

The electrical properties of MIS InP diodes where the interfacial layer is prepared by electron beam evaporation of Ta and subsequent rapid thermal oxidation of evaporated Ta film are studied. Ta and Al are used as the gate metals. Compared with the case of no interfacial film between metal and InP, the barrier height increases by 0.22 and 0.12 eV for Ta and Al gate metals, respectively. The MIS diode with Ta gate metal shows good thermal stability. In the case of Al gate metal the thermal stability is poor.

Linear and nonlinear analysis of microwave power generation in submicrometer n+nn+ InP diodes

A closed hydrodynamic model and the associated numerical procedures are developed for simulating hot-carrier transport in submicron semiconductor devices. To check the validity of the model, the steady-state characteristics of near-micron n+nn+ InP diodes are compared with a standard Monte Carlo approach. The excellent agreement found fully validates the physical reliability of our model which has been further developed to investigate linear and nonlinear time-dependent characteristics. The contribution of each part of the device, when operating as microwave power-generation, is analyzed through the spatial profiles of the impedance-field spectrum. The usual subdivision of the n-region into a passive (dead-zone) and active zone is carried out. The dead zone is found to manifest itself as a purely real resistance which is practically independent of the frequency. One or more spatial zones which are responsible for the generation are shown to be formed in the active region of the diode. By reducing the length of the n-region, under the condition that the total current is constant in time, the additivity of the contributions from each part of the device into the generation spectrum is proven. The predictions of the linear analysis are compared with a direct simulation of the diode performance in the external resonant circuit. A wide-band tuning of the generation frequency from 100 up to 200 GHz is demonstrated. The microwave power generation is shown by both hydrodynamic and Monte Carlo simulation to be caused by the formation and propagation through the diode of accumulation layers. Theoretical results are found to compare well with available experiments.

Electronic noise and impedance field of submicron n+nn+ InP diode generators

We investigate the electronic noise and impedance field of submicron n+nn+ diode generators when loaded by an external resistance in the framework of a Monte Carlo and a hydrodynamic simulative approach. We observe a long-time oscillation of the correlation function of the voltage drop fluctuations between the resistor terminals. The oscillations are in turn responsible for a peak in the noise power-spectrum which is caused by the spontaneous formation of electron accumulation layers. The drift of these layers through the n-region is monitored for biasing conditions above threshold for microwave generation. The frequency of the noise peak is shown to correspond to the highest generation frequency for the given load resistance. The noise power-spectra calculated for three different values of the load resistance are used to obtain the small-signal and noise characteristics of the intrinsic unloaded diode. The parallel hydrodynamic calculation of the diode impedance spectrum is found to compare well with the results obtained from the noise analysis of the Monte Carlo simulation.

Calculation of shift of avalanche transit time phase delay due to optically injected carriers in indium phosphide avalanche diodes

A computer method for the calculation of the phase shift due to optically injected carriers in an InP avalanche transit time diode has been suggested using the numerically simulated negative resistance profiles in the depletion layer of the diode. The results show that the phase shift due to hole injection is larger than that due to electron injection which explains the pronounced effect of photogenerated hole leakage current in modulating the microwave properties of InP diodes.

Noise and impedance of n+-n-n+ InP microwave generators

The noise power spectral density Pn in a submicron InP diode loaded by resistor R is calculated using the Monte Carlo particle technique. It is shown that at biases above the generation threshold the Pn has a peak at the frequency fpeak which corresponds to the highest generation frequency at the given R. The excess noise is the shot noise of electrons accumulated into the layers. Measuring the frequency of the peak fpeak as the function of R one can obtain the negative values of the real part of impedance at the high-frequency side of the negative impedance spectrum.

Response functions in submicrometre n+nn+ diode generators

A closed hydrodynamic approach based on the system of conservation equations for carrier number, drift velocity and mean energy coupled with the Poisson equation is used to calculate the response functions in the time domain of the local electric field and applied voltage for a near-micrometre n+nn+ InP diode. By Fourier analysis, the generation bands in the frequency domain are then obtained. The good agreement achieved with available experiments validates the present theoretical approach. A significant increase of the cut-off frequency of the microwave power generation up to 600-700 GHz is predicted for submicrometre GaAs and InP diodes.

Submillimeter wave generation and noise in InP diodes

High-frequency (350–750 GHz) generation in submicrometer InP diodes is investigated by modified hydrodynamic and Monte Carlo particle (MCP) techniques. The noise power spectral density Pn in the diode loaded by resistor R and generation spectra Pg in a series resonant RL circuit are calculated using the MCP technique. It is shown that at the biases above the generation threshold the Pn has a peak at the frequency fmax which corresponds to the highest generation frequency at the given R. The excess noise arises in the frequency region where the real part of diode impedance Re Z has negative values. At the bias below the generation threshold (i.e., when Re Z is positive over entire frequency range) the Pn(f) has the usual Lorenzian shape. The MCP simulation of Pg for 0.25-μm-length diode shows the Gaussian shape of the spectra at frequencies 517 and 622 GHz. The Pg broadening at higher frequencies is the result of interaction between the self-oscillations at frequency fmax and circuit-driven oscillations.

Impedance field and microwave power generation in InP diodes

A closed hydrodynamic (HD) approach is used to carry out a comprehensive spatial analysis of the dynamic features of submicron n+ nn+ InP diode both in time and frequency domains. The contribution of each part of the device, when operating as microwave power generator, is analyzed through the spatial profiles of the impedance-field spectrum. The usual subdivision of the n-region into a passive (dead-zone) and active zone is carried out. The dead zone is found to manifest ittelf as a purely real resistance which is practically independent of the frequency. One or more spatial zones which are responsible for the generation are shown to be formed in the active region of the diode. By reducing the length of the n-region, under the condition that the total current is constant in time, the additivity of the contributions from each part of the device into the generation spectrum is demonstrated.

Monte Carlo simulation of hot carrier noise in short n+nn+ diodes

The Monte Carlo method is applied to calculate the current and voltage noise in near micron n+nn+ InP diodes. Quite different behavior of the correlation functions and spectral densities of fluctuating macroscopic quantities is observed under the voltage and current driven operations. Under the constant voltage operation the time dependence of the current fluctuation correlation function exhibits damped oscillations at the transit-time and plasma frequencies. This results in appearance of two spikes in the current noise spectrum at corresponding frequencies. The transit-time oscillations and the corresponding noise are shown to be caused by the spontaneous formation of electron accumulation layers due to the negative differential resistance connected with the combined action of the velocity overshoot and Gunn-effects. In the contrast, the voltage noise spectrum is found to have a regular Lorentzian shape under the constant current operation. The observed features of the current and voltage noise spectra are shown to be in a good agreement with the frequency dependence of the small-signal admittance and impedance of the diode.

Current Transport in Cryogenic Processed Metal/InP and GaAs Interfaces

ABSTRACTSchottky contacts to n type InP and GaAs have been made by deposition on substrates cooled to low temperature (LT=77K) in a vacuum close to 10-7 Torr.The Schottky barrier height, ФB, was found to be as high as 0.96eV with Pd/InP and 0.95eV for Au/GaAs. This indicated a significant increase in ФB compared with the room temperature (RT=300K) deposition. For diodes fabricated at room temperature, the reverse saturation current density, JO, decreased sharply with decrease in measuring temperature. For the RT InP diodes, the conduction mechanism was controlled by thermionic emission (TE). For the LT InP diodes, the value of JO was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15eV, with a temperature coefficient of -3.2 x 10-4 eV/K. The forward transport mechanism was controlled by thermionic field emission (TFE). For the GaAs diodes, thermionic emission (TE) dominated in the current transport at room temperature for both RT and LT diodes. At low testing temperature, RT diodes exhibited an excess current component at low forward bias.

Submillimeter wave low-temperature admittance of n-GaAs and n-InP diode structures

Numerical simulation results for n+nn+ GaAs and InP diode structures in the 1–5 THz frequency range are presented. Cryogenic temperatures from 4 through about 77 K as well as some cases above liquid-nitrogen temperature are examined to obtain the two-terminal admittance. Earlier work has suggested possible negative conductivity at or below 4.2 K, but nothing consistent above 77 K. Implications of the Monte Carlo data for generation of submillimeter waves at intermediate lattice temperatures between 4 and 60 K are discussed for GaAs. Furthermore, numerical results are obtained at elevated lattice temperatures (200 and 300 K) to form a more complete view of transport in InP. The GaAs and InP results strongly suggest negative conductance behavior will be found below 20 K.

Reply to ‘‘Comment on ‘Current transport in Pd/n-InP diodes formed at room and low temperature’ ’’ [J. Appl. Phys. 72, 3803 (1992)

A further analysis of our previous data [Z. Q. Shi and W. A. Anderson, J. Appl. Phys. 72, 3803 (1993)] suggests conduction by thermionic field emission at low voltage for Au or Pd/n-InP Schottky diodes fabricated by cryogenic processing or low temperature (LT). Data at higher voltages follow the thermionic emission mechanism as described by R. T. Tung, J. Appl. Phys. 73, 4064 (1993). We do not feel that the inhomogeneity model of Tung should be applied to the LT diode due to the nature of thin film formation for metals deposited at low temperature.

Comment on ‘‘Current transport in Pd/n-InP diodes formed at room and low temperature’’ [J. Appl. Phys. 72, 3803 (1992)

It is pointed out that, under most circumstances, current transport characteristics observed at Schottky barrier junctions cannot be used to unambiguously identify the mechanism responsible for electron conduction. This practice, however, is quite common and is shown to lead to an incorrect conclusion in a recent article [Z. Q. Shi and W. A. Anderson, J. Appl. Phys. 72, 3803 (1992)].

Current transport in Pd/n-InP diodes formed at room and low temperature

Schottky contacts to n-InP have been made by deposition on substrates cooled to low temperature (LT=77 K) with a vacuum close to 10−7 Torr. The Schottky barrier height, φB, was found to be as high as 0.96 eV with Pd metal. This indicated an 0.4 to 0.5 eV increase in φB compared with the room temperature (RT=300 K) deposition. For the diode fabricated at room temperature, the reverse saturation current density, J0, decreased sharply with the decrease of measuring temperature. The φB was increased from 0.48 to 0.71 eV, with the testing temperature decreased from 300 to 100 K, with a temperature coefficient of −6.1×10−4 eV/K. The conduction mechanism was controlled by thermionic emission. For the LT diode, the value of J0 was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15 eV, with a temperature coefficient of −3.2×10−4 eV/K. The forward current had a saturation trend at a larger forward bias. In this region, the current was almost temperature independent and the transport mechanism was controlled by thermionic field emission.

A generalized simulation method for MITATT-mode operation and studies on the influence of tunnel current on IMPATT properties

A generalized method of DC and high-frequency analysis for microwave transit time diodes in mixed tunnelling and avalanche mode, which can be applied to any type of diode structure is reported. Taking a purely field-dependent tunnel generation rate for electrons, the same is computed for holes from a simulated energy band diagram within the depletion layer of the diode. The method has been applied to a variety of Si, GaAs and InP diode structures. The results show a substantial degradation of IMPATT properties due to phase distortion caused by the tunnelling current.

Influence of dislocation density on I-V characteristics of InP photodiodes

The influence of dislocation density on the I-V characteristics of InP diodes under reverse bias has been investigated. It is observed that the leakage current increases with increasing dislocation density whereas the breakdown voltage is reduced. Further, precipitates are observed on dislocations in the p-regions formed by the in-diffusion of Cd into n-type InP layers. It is argued that the increase in leakage current is due to the presence of space charge cylinders around dislocations threading the p-n junction. On the other hand, precipitates may be responsible for premature avalanche breakdown. In addition, for the range in energy scanned, levels within the bandgap due to dislocations are not observed by photoluminescence measurements.

Electrical properties of distributed electron cyclotron resonance plasma-deposited SiO2-InP diodes

Low-temperature deposition (room temperature, RT-250 °C) of high-resistivity SiO2 layers has been successfully developed on InP substrates. Complete electrical characteristics of metal-insulator-semiconductor (MIS) diodes show promising characteristics in terms of barrier height at the SiO2-InP interface and in terms of interface state distribution (NSS). Leakage current is essentially bulk limited (ρ=4×1015 Ω cm) until a high electrical field in the range 4–6 MV cm−1 and a minimum value of NSS of 2×1011 cm−2 eV−1 range is achieved, without particular surface treatment. These results show that the technique is well adapted to n-type depletion-mode MIS field-effect transistor processing.