摘要:

The first successful demonstration of long wavelength infrared (LWIR) detection with a photovoltaic‐type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is centered near 10 μm in good agreement with the theoretical response band provided that electron–electron interactions are taken into account. The detector operates at significantly lower bias voltage than photoconductive multiple quantum well LWIR detectors. This could lead to important advantages in applications to photovoltaic detector arrays. Optimization through the use of termination layers at the ends of superlattices is also discussed. The response at 83 K is about 50% of the response at 24 K which is 5 mA/W. Optimization of the response, operating temperature or bias voltage has not been carried out.

ISSN:1071-1023    

DOI:10.1116/1.585800

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We report in this article, for the first time the performance of light emitting diodes (LEDs) made in HgCdTe (MCT) epilayers on CdZnTe (CZT) lattice‐matched substrates grown either by liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE). Diodes aren/phomojunctions made by ion implantation. The MCT composition was chosen in order to get the emission wavelength between 3 and 5 μm. Electroluminescence spectra were recorded between 20 K and 300 K. A comparison of the two materials is made, demonstrating that they exhibit similar performances. Internal quantum efficiencies as high as 25% (λ peak=4.1 μm at 77 K) and 6% (λ peak=3.5 μm at 300 K) were obtained on both LPE and MBE materials and they reach a maximum for a temperature of about 90 K. For a material with λ peak=5.5 μ at 77 K, internal quantum efficiency remains as high as 5%. The external quantum efficiency is considerably increased using backside emission through the CZT substrate and optical coupling with a CZT lens: in such conditions 20% of the emitted light could be extracted from the structure. These results show that MCT can already be used for LEDs in the 3–5 μm region.

ISSN:1071-1023    

DOI:10.1116/1.585801

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Growth of modulation‐doped HgTe–CdTe superlattices (SLs) at very low temperatures (140 °C) by photoassisted molecular beam epitaxy is reported. SL layer thicknesses were intentionally chosen such that most of the SLs studied are inverted‐band semimetals or inverted‐band semiconductors. Bothp‐ andn‐type samples were successfully prepared and studied. The doped superlattices exhibit excellent electrical properties. Lack of carrier freeze‐out at low temperatures provides convincing evidence that modulation‐doping has been achieved.

ISSN:1071-1023    

DOI:10.1116/1.585802

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Low temperature infrared transmission and far‐infrared magneto‐optic transmission experiments were completed for a series of HgTe/CdTe superlattices (SLs). The SLs studied were grown with layer thicknesses intentionally chosen to make the samples inverted‐band semimetals or inverted‐band semiconductors, a new regime of the HgTe/CdTe SL which only recently has been predicted by theory. Cyclotron resonance of electrons in the first conduction subbandH1 was observed in the far‐infrared magneto‐transmission experiments. From these measurements electron effective masses were calculated. The optical transition from the second heavy hole subbandH2 to the second conduction subbandE2 was observed in the infrared transmission experiments. TheH2–E2 transition energy was observed todecreasewithincreasingSL well widthLZ. In addition, the electron effective mass was found toincreaseasLZincreases. Both of these observations indicate that all of the SL samples are, indeed,inverted‐bandSLs. This in turn implies that the valence band offset between HgTe and CdTe must be large, ∼400 meV at 4.5 K.

ISSN:1071-1023    

DOI:10.1116/1.585803

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Magneto‐optical transitions induced by the coupling between the conduction and the valence bands through the momentum matrix element, and by the coupling terms between light and heavy holes resulting from an applied magnetic field are studied theoretically in narrow gap HgTe–CdTe superlattices. Selection rules and transition probabilities for the above transitions are presented and compared with allowed transitions. The numerical results for the transition probabilities show that some of the interband transitions with ΔN=±1 are significant and have to be considered in the studies of interband magneto‐optical spectra of narrow gap superlattices.

ISSN:1071-1023    

DOI:10.1116/1.585804

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have investigated quantum oscillations in the magneto‐transport properties of HgTe–CdTe superlattices grown by molecular‐beam epitaxy. Modulation doping was achieved by incorporating either indium donors or arsenic acceptors into the CdTe barriers. In ap‐type sample, quantized plateaus were observed in the Hall conductivity down toi=3 conduction channels. Since the structure contained 200 periods, this implies that the quantized holes populated only a small fraction of the total superlattice volume. A mixed conduction analysis of the nonoscillating component of magneto‐transport data provided confirming evidence for the presence of a two‐dimensional hole gas with the appropriate density in addition to the superlattice holes. Previous reports of the quantum Hall effect in HgTe–CdTe also yieldedifar less than the total number of superlattice wells. In contrast, ann‐type sample from the present study displayed a single quantum Hall plateau ati≊140, indicating that in this case most of the 200 superlattice periods contributed to the conduction. We argue that this represents the first observation of the quantum Hall effect associated with carriers distributed throughout the interior of a HgTe–CdTe superlattice.

ISSN:1071-1023    

DOI:10.1116/1.585805

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We present results of the first detailed theory for electron and hole transport in HgTe‐CdTe superlattices. The calculation incorporates the superlattice band structure in full generality, and also treats multi‐well scattering and screening processes which have been ignored in previous theories. It is predicted that whereas the electron and hole mobilities should be nearly equal at low temperatures, the hole mobility falls far below the electron value at somewhat higher temperatures due to the extreme nonparabolicity of the valence band. This prediction is entirely consistent with experimental results reported previously. Excellent quantitative agreement with the data over a broad temperature range is achieved if interface roughness scattering is considered in addition to ionized impurity scattering, acoustic and optical phonon scattering, and electron–hole scattering. It is pointed out that low‐temperature electron mobilities for a number of thin‐well HgTe–CdTe superlattices follow thed6Wdependence expected for the interface roughness mechanism.

ISSN:1071-1023    

DOI:10.1116/1.585806

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Metalorganic chemical vapor deposition (MOCVD) growth of HgCdTe on GaAs is a promising technique that overcomes the size and crystal quality limitations of CdTe substrates. An important material parameter is the minority carrier lifetime, which determines the ultimate zero bias impedance and quantum efficiency of a photodiode. We present the first systematic study of the temperature and carrier concentration dependence of minority carrier lifetimes onn‐type andp‐type layers of MOCVD long‐wavelength infrared HgCdTe grown on GaAs substrates. The temperature dependencies of the lifetime are compared with theoretical predictions based on Auger, radiative, and Shockley–Read recombination. Excellent fits are obtained over a broad temperature range, from 20 K to room temperature. The experimental lifetimes ofn‐type material reach the theoretical limit imposed by Auger+radiative recombination for carrier concentrations higher than 2×1015cm−3. For lower carrier concentrations, the measured lifetimes are shorter than those predicted from Auger+radiative recombination, and Shockley–Read recombination must be added to the calculations. The lifetimes of arsenic‐doped and vacancy‐dopedp‐type material are Shockley‐Read limited. They are one order of magnitude longer than those previously observed on vacancy‐doped liquid phase epitaxy material.

ISSN:1071-1023    

DOI:10.1116/1.585807

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Carrier trapping influences the performance of HgCdTe infrared detectors in the 8–12 μm range by enhancing tunneling currents, reducing excess carrier lifetimes, and increasingg–rand 1/fnoise. In this work, the effects of carrier trapping on the tunneling currents inn+pdiodes are calculated, and the dependence of the tunneling current on temperature, bias, doping level, and trap characteristics is illustrated. It is shown that by assuming the dominant trap energy to be at the Fermi level, the calculated tunneling currents exhibit many of the peculiar features which have been observed experimentally. The related effects that minority carrier traps have on the excess carrier lifetimes are also discussed, and a simple method of estimating many of the relevant trapping characteristics from lifetime measurements is presented.

ISSN:1071-1023    

DOI:10.1116/1.585808

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Synchrotron x‐ray topography studies have been conducted at the National Synchrotron Light Source at Brookhaven National Laboratory to correlate defects in HgCdTe epilayers with those in underlying CdTe family substrates. Infrared detectors have been fabricated on these epilayers to investigate the performance impact of specific defects. This paper describes synchrotron x‐ray facilities and methods. Images of substrates and epilayers are discussed and mapping of epilayer/substrate defects, such as microtwins, subgrain boundaries and slip lines, is demonstrated. Efforts to map detector array performance to epilayer and substrate topographs are described.

ISSN:1071-1023    

DOI:10.1116/1.585809

出版商:American Vacuum Society    

年代:1991

数据来源: AIP