Fabrication Of HgCdTe APD And Research Of Noise

The HgCdTe avalanche focal plane device has the characteristics of multi-function,active/passive dual mode and high sensitivity required by the third generation infrared focal plane detector.It has shown strong application potential in low-light flux detection,hyperspectral,active-passive composite imaging,and free-space communication.This paper has carried out a series of research work on two aspects:device fabrication and noise research.All works are summarized as follow:1.Research on ion beam etch rateEtch rate of CdTe is 0.98nm/s?etch parameters:accelerate voltage 100V,beam voltage 200V,beam current 250mA?.Etch rate of ZnS is 0.07nm/s?etch parameters:accelerate voltage 50V,beam voltage 100V,beam current 125mA?.May be due to equipment that the actual etch rate does not match the Smoekh theoretical model,therefor we proposed an empirical formula for the etch rate of ZnS with acceleration voltage in the range of 100V²20V,beam voltage/beam current in the range of100V/125mA²00V/250mA:ER=0.00014?0.014V_?-0.399??0.024V_?-1.407?.We found that etch rate must be decressed to control the thickness of N-type layer accurately.So,the key of IBM is consistent thickness of dielectric film.2.Research on the thickness and concentration of N-type layer formed by IBM and horizontal expansion of carriers.The depth and concentration distribution of the N-type layer formed by different etching conditions were studied by the differential hall test.Then the ion beam etching conditions of acceleration voltage 50V,beam voltage 100V and beam current 125mA were determined.By such etching conditions,P-type material with a Hg vacancy concentration of 1.3×10 ¹⁶ cm^-3 will form a 5?m thickness N-type layer,wherein the carrier concentration in the surface of 1?m is on the order of 10¹⁶ cm^-3,and the carrier concentration of about 4?m is on the order of 10¹⁵ cm^-3.The LBIC test results show that the horizontal expansion of the carrier is also related to the size of the etched region.The larger the etched region,the more horizontal expansion.3.A multilayer carrier model in HgCdTe was established.It can be used to analyze the electrical parameters such as carrier concentration and mobility at different depths in the differential hall test.4.Device fabrication and performance test of HgCdTe APD.A planar PIN HgCdTe APD device was successfully fabricated by IBM.The results show that the gain is closely related to the cut-off wavelength and N^-region thickness.A gain of 1200 at a bias of 17.5V was achieved in an HgCdTe APD with a cutoff wavelength of 4.8?m.The APD device excess noise factor is positively correlated with the reverse voltage.We also fabricat the first HgCdTe APD FPA device in China with cutoff wavelength 3.56?m and 16×16 pixels.The operability in gain exceeds 90%and relative gain dispersion is lower than 20%under the reverse bias of0⁶V.NEPh is about 60 at 6V bias with excess noise factor close to 1.2.Quantum efficiency at 10V is 91.75%at 10V.5.Build a low frequency noise test system.The background noise level of the test system is approximately 2×10^-28 A²/Hz,which is lower than the current device noise level and can be used to characterize the noise level of existing devices.The low-frequency noise components of common HgCdTe diode and HgCdTe APD are studied.The common HgCdTe diode exhibit 1/f noise,generation-recombination noise and white noise under small reverse bias.With the increase of the reverse bias voltage,the 1/f noise gradually increases,indicating that the surface leakage current gradually becomes larger.The noise level of the HgCdTe APD is significantly larger than former,and the noise component is also dominated by1/f noise.The noise test results show that surface leakage current is an important reason that limits the performance of current devices.6.Introduce some new structure and new processes into the HgCdTe APD device Fabrication.A mesa device with a cutoff wavelength of 4.4?m was fabricated with a maximum gain of 80 at 7.5V reverse bias.We research in the junction properties with CdTe as the injection barrier and propose a empirical formula of B⁺:The effect of annealing on the depth of PN junction was studied.The PN junction depth formed by the energy of 150keV and the dose of 1×10¹⁴cm^-22 was 1.36?m¹.65?m,and the junction depth after annealing was 2.41?m².82?m.While the injection dose was increased to 1×10¹⁵cm^-2,there was no obvious change in the properties of the junction region,indicating that the carrier concentration is saturated at the injection dose of 1×10¹⁴cm^-2.