Reverse Bias Dark Current Research Articles

MBE growth and characterization of doped multiple quantum well avalanche photodiodes

In the present study, how certain growth, processing and surface treatment techniques can be used to dramatically lower the dark current behavior of APDs by several orders of magnitude and improve the depletion characteristics of the built-in structures is shown. Through careful dopant calibration, the devices could be grown such that they were essentially fully depleted as grown, even though doping levels in the avalanche region were in the low 10 18 cm -3 . The full depletion characteristics of the APDs were verified using theoretical modeling conducted for devices with similar structure and doping profiles. After processing the devices into mesa diodes, various surface passivation treatments were investigated These include both 02 plasma and sodium sulfide treatments. Through the application of such treatments, a decrease in the reverse bias dark current by as much as a factor of 1000 was achieved. Dark currents as low as 1 pA were obtained near zero bias. In some APDs, the dark currents increased to only 12 pA at 20% of breakdown. In addition, these devices exhibited extremely high gains, which exceeded 35006 in some APDs. The effect of the dopant profile in the avalanche region was also investigated. It was found that by the proper choice of dopant density and separation the break down voltage of the devices could be reduced by as much as 25%.

Piezoelectric effects in HgCdTe devices

Piezoelectric effect in long-wavelength infrared (LWIR) HgCdTe has been studied using metal-insulator-semiconductor (MIS) and p-n homojunction devices. A cantilever beam technique was used to measure the shift in flatband voltage in the MIS devices as a function of applied strain, from which piezoelectric constant was derived. This is the first time such a value has been reported in the literature. Subsequent calculation showed that the thermal stress from cryogenic cool (from 300 to 77K) of hybridized infrared devices fabricated on (111) HgCdTe surfaces induced a piezoelectric field of∼1840 V/cm. This field is present in the space charge regions in the semiconductor where there is no free carrier. It reinforces the built-field in an n-on-p diode fabricated on the (111)A HgCdTe surface. Thus, the diode is more prone to the thermal stress than one fabricated on the (lll)B surface. Electrical measurement of reverse-bias dark currents in HgCdTe photodiodes under applied compressive and tensile stress confirmed the existence of a strain-induced field in the junction.

Excess currents in narrow gap Cd xHg 1−xTe p-n junctions

Reverse bias dark currents in p-n junctions fabricated in undoped Cd x Hg 1− x Te (CMT) (0.22 < x < 0.24) LPE epilayers by ion implantation of boron have been studied at different temperatures. The behaviour of current-voltage ( I–V) characteristics at temperatures below 80 K allows us to discriminate two types of material. The first group consists of samples with currents dominated by a band-to-band tunnelling mechanism. The second is characterized by the current which exceeds that in the first group. The excess currents proved to be connected with fluctuations of charged impurity density which changed local tunnel transparency of the potential barriers. This mechanism is likely to dominate current in closely compensated samples. A quantitative analysis of I–V characteristics is made.

Using reverse bias currents to differentiate between bulk degradation and interfacial degradation in hydrogenated amorphous silicon p-i-n structures

The ‘‘analysis of microelectronic and photonic structures’’ (amps) transport-simulation computer program has been used to show that a distinction can be made between the effects of light-induced bulk and interfacial degradation in hydrogenated amorphous silicon (a-Si:H) p-i-n detector and solar cell structures. Using reverse bias leakage (dark) currents, amps simulations show that, for p and n layers that do not allow significant injection of electrons and holes into the intrinsic layer of the p-i-n structure, a light-induced increase in the density of interfacial states will result in significantly different changes in the voltage behavior of the reverse bias dark currents than will a corresponding increase in the density of bulk defect states. This communication demonstrates that a careful study of the reverse bias dark currents can provide an excellent means of determining if light soaking of a-Si:H p-i-n devices results in bulk degradation, interfacial degradation, or both.

Observation of novel steplike structure in the photocurrent and dark current of a superlattice: Charge collection by successive depletion of quantum wells

We have observed novel manifestations of superlattice properties in a Ga0.47In0.53As/InP quantum well photodiode structure grown by gas source molecular beam epitaxy, evident as multiple steps in the reverse bias photocurrent and dark current. This striking effect is explained in terms of depletion of successive quantum wells as the reverse bias field is increased, while the diffusion of carriers generated in the undepleted region is suppressed by localization within the wells. As the electric field punches through into each well the carriers photogenerated and thermally generated in that well are collected by the field, while carriers generated in the undepleted wells remain localized and cannot contribute to the current. This causes a steplike increase in the photocurrent and the dark current.

Low dark current GaAs/AlAs graded-parameter superlattice PIN photodetector

Preliminary measurements of the photoresponse of a GaAs p-n junction containing an undoped asymmetric GaAs/AlAs superlattice are presented. Very low reverse-bias dark currents (<6×10?8 A/cm2 at 3 V) are measured, while still retaining the speed and spectral response of a conventional GaAs PIN diode. The ?3 dB bandwidth is found to be greater than 1 GHz, and the responsivity is 0.1 A/W.