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A copper‐related shallow acceptor complex has been discovered in germanium single crystals grown in vacuum and doped with arsenic and copper. Photothermal ionization spectroscopy of samples quenched from 673 K reveals two sets of hydrogenic lines with ground state binding energies of 9.15 and 10.05 meV. The line intensity ratios between corresponding transitions (1s‐np) of the two hydrogenic series follow a Boltzmann dependence. This shows that the two series belong to the same impurity complex with a split ground state. Taking into account the crystal growth conditions together with the changes in the donor concentration deduced from variable temperature Hall effect measurements, we conclude that arsenic and substitutional copper form the new acceptor complex A(Cus,As) since copper is the only fast‐diffusing species at this low annealing temperature. This complex is expected to have C3v symmetry in agreement with preliminary piezospectroscopy measurements.

We present strong experimental evidence suggesting that we have synthesized the \ensuremath{\beta}-${\mathrm{C}}_{3}$${\mathrm{N}}_{4}$ phase. This is a material predicted by theory to have bulk moduli comparable to diamond. Thin films containing small crystals were deposited on Si and Ge wafers by rf diode sputtering of a pure graphite target with pure ${\mathrm{N}}_{2}$. The crystal structure of these phases was investigated using x-ray and electron-beam diffractometry as well as transmission electron microscopy. Our results indicate that the \ensuremath{\beta}-${\mathrm{C}}_{3}$${\mathrm{N}}_{4}$ particles with typical dimensions of \ensuremath{\sim}0.5 \ensuremath{\mu}m are embedded in a 1-\ensuremath{\mu}m-thick layer of a C-N polymer. These particles are believed to crystallize preferentially on Si (100) wafers.

Far‐infrared properties of a two‐layer structure consisting of an ion‐implantation doped layer on a thin ultrapure slice of germanium have been studied. Photoresponse extends beyond the shallow impurity absorption edge at 120 μm to about 192 μm. Photoconductivity studies have been performed between 4.2 and 1.3 K. Detectors with an area of 1×1 mm2 have dark currents of less than 100 electrons/s at temperatures ≤1.3 K at a bias of 70 mV. A responsivity of 0.9 A/W and a noise equivalent power of 5×10−16 W/Hz1/2 have been measured using photons in a narrow band 99±0.5 μm.

We report on the development of Germanium Blocked Impurity Band (BIB) photoconductors for long wavelength infrared detection in the 100 to 250.μm region. Liquid Phase Epitaxy (LPE) was used to grow the high purity blocking layer, and in some cases, the heavily doped infrared absorbing layer that comprise theses detectors. To achieve the stringent demands on purity and crystalline perfection we have developed a high purity LPE process which can be used for the growth of high purity as well as purely doped Ge epilayers. The low melting point, high purity metal, Pb, was used as a solvent. Pb has a negligible solubility 17 cm−3 in Ge at 650°C and is isoelectronic with Ge. We have identified the residual impurities Bi, P, and Sb in the Ge epilayers and have determined that the Pb solvent is the source. Experiments are in progress to purify the Pb. The first tests of BIB structures with the purely doped absorbing layer grown on high purity substrates look very promising. The detectors exhibit extended wavelength cutoff when compared to standard Ge:Ga photoconductors (155 μm vs. 120 μm) and show the expected asymmetric current-voltage dependencies. We are currently optimizing doping and layer thickness to achieve the optimum responsivity, Noise Equivalent Power (NEP), and dark current in our devices.

We demonstrate a reversible phase transition in nanoparticles composed of a binary eutectic alloy, Ge–Au. The structure, 9 nm diameter nanoparticles embedded in silica, can be switched from bilobe to mixed using a 30 ns ultraviolet laser pulse. The structure can be switched back to bilobe by heating at 80 °C. The bilobe/mixed switching can be performed on the same sample at least ten times. Synchrotron X-ray diffraction studies reveal that the bilobe structure contains crystalline Ge and Au while the mixed structure consists of crystalline Ge and β Ge–Au.

Extrinsic far-infrared photoconductivity in thin high-purity germanium wafers implanted with multiple-energy boron ions has been investigated. Initial results from Fourier transform spectrometer(FTS) measurements have demonstrated that photodetectors fabricated from this material have an extended longwavelength threshold near 192μm. Due to the high-purity substrate, the ability to block the hopping conduction in the implanted IR-active layer yields dark currents of less than 100 electrons/sec at temperatures below 1.3K under an operating bias of up to 70mV. Optimum peak responsivity and noise equivalent power(NEP) for these sensitive detectors are 0.9A/W and 5×10−16 W/Hz1/2 at 99μm, respectively. The dependence of the performance of devices on the residual donor concentration in the implanted layer will be discussed.

Surface states on germanium p-i-n junctions have been investigated using deep level transient spectroscopy (DLTS) and collimated beams of 60 keV gamma-rays. The DLTS spectra have a characteristic signature for each surface treatment but the spectra are complex and not readily interpretable as to suitability for radiation detectors. Collimated gamma-ray beams give a direct measure of surface channel effects and typeness. Hydrogenated amorphous germanium (a-Ge:H) was explored as a surface layer to adjust the electrical state and passivate the surface. Our measurements show that these layers produce flat band conditions, introduce no additional noise and appear to be stable against a variety of ambients.

A broad review of the physics of point defects, i.e. electrically active and neutral impurities and impurity complexes is given. Basic material science which is crucial for understanding the physics is summarized in an introductory section. It is followed by the detailed description of the novel measurement techniques—photothermal ionization spectroscopy, high-Q electron paramagnetic resonance and deep level spectroscopy. These spectroscopic techniques have had a profound impact on the investigations of ultra-pure germanium. The major part of this work deals with the physics of point defects in ultra-pure germanium. The high purity of this semiconductor allows the undisturbed observation of highly excited bound states of shallow donors and acceptors. Many new previously unknown acceptor and donor centres have been discovered in ultra-pure germanium. The nature of several of these centres can be understood in terms of a complex consisting of two impurities—a light interstitial atom (for example, h...

Using 14C-spiked pyrolytic graphite-coated quartz crucibles for the growth of nine ultra-pure germanium single crystals, we have determined the carbon content and distribution in these crystals. Using autoradiography, we observe a rapidly decreasing carbon cluster concentration in successively grown crystals. Nuclear radiation detectors made from the crystals measure the betas from the internally decaying 14C nuclei with close to 100% efficiency. An average value for the total carbon concentration [14C+12C] is ~2×1014cm-3, a value substantially larger than expected from earlier metallurgical studies. Contrary to the most recent measurement, we find the shape of the beta spectrum to agree very well with the statistical shape predicted for allowed transitions.

High-purity germanium crystals used for making nuclear radiation detectors are usually grown in a hydrogen ambient from a melt contained in a high-purity silica crucible. The benefits and problems encountered in using a hydrogen ambient are reviewed. A hydrogen concentration of about 2×1015cm-3 has been determined by growing crystals in hydrogen spiked with tritium and counting the tritium s-decays in detectors made from these crystals. Annealing studies show that the hydrogen is strongly bound, either to defects or as H2 with a dissociation energy > 3eV. This is lowered to 1.8eV when copper is present. Etching defects in dislocation-free crystals grown in hydrogen have been found by etch stripping to have a density of about 1×107cm-3 and are estimated to contain 108H atoms each.

Techniques have been developed to consistently purify germanium to the 1010 atoms/cm3 range. The major impurities are the acceptors boron and aluminum and the donor phosphorous. Formation of nonsegregating compounds of boron and aluminum make these elements difficult to remove by conventional zone refining whereas phosphorous and all other electrically-active impurities segregate normally and are therefore removed in the zone refining process. The only significant impurity introduced in our Czochralski crystal puller is phosphorous whose source has been traced to the quartz crucible. To reliably reduce impurity concentrations to acceptable levels it has been necessary to develop techniques for determining the types and concentrations of impurities in both the final single crystals and in the polycrystalline zone-refined ingots and to relate these results to the use of various boat and crucible materials. Photothermal Ionization Spectroscopy and electrical measurements have been used to identify and measure the impurities.

This paper describes a valuable tool for tracing the origins of impurities introduced into high-purity germanium during the zone-refining and crystal growing processes. Small single crystals are located in the polycrystalline zone-refined ingots by chemical etching techniques and the concentration and type of residual impurities in these crystals are determined by Hall effect, conductivity measurements and photothermal ionization spectroscopy. Results are presented which indicate that the common impurities boron, aluminum and gallium all segregate more slowly in zone refining than is predicted by simple theory. This anomaly is attributed to compound formation involving the impurities and the zone-refining boat material.

The excitation spectra of shallow acceptors in ultra-pure germanium (109 cm-3 < NA − ND < 1012 cm-3 were studied using Fourier Transform Spectroscopy and photothermal excitation. Using samples with a total number of less than 108 acceptor atoms, the signal to noise ratio was better than 100. In the purest samples the natural width of some excited states was found to be below the instrumental resolution of 0.03 meV (= 0.25 cm-1). Some new observations involve the resolution of lines of states near the top of the valence band and the discovery of two unknown shallow acceptors.

The present state of our knowledge of the properties of high purity germanium is reviewed. The role of excess vacancies, oxygen and high dislocation density in producing trapping in detectors is discussed. By the application of Fourier Transform Spectroscopy, the major impurities have been identified and aluminum has been found to be the dominant one in most crystals. Analysis has shown that the principal source of aluminum is the polycrystalline starting material. The material problems related to detector fabrication are surveyed and a spectrum taken with a 43 cm3 coaxial detector is presented. It is concluded that the important problems of material development are well delineated but that their solutions will require intensified effort.

This note establishes the value of observation of etch-pit distributions as a guide in the selection of germanium for use in lithium-drifted germanium detectors. Results are presented showing a very good correlation between the etch-pit distribution and detector performance for a number of crystals pulled on the 111 axis. It is inferred that mechanical strain produced by thermal conditions in the crystal growing process is the major source of potential charge trapping sites in the final detector.

A critical examination of observations on high-purity germanium exhibiting acceptor concentrations in the 1010/cm3 range, indicates that the acceptors are probably due to lattice defects such as vacancy clusters. The paper presents evidence to support this contention.

Drifting a thick lithium-drifted counter (silicon and germanium) is a time-consuming operation that frequently results in a poor device, owing to inadequate knowledge of progress of the drifting operation. The drifting apparatus described here automatically controls the temperature of the detector that is being drifted to maintain the leakage current at a preselected value. While drifting proceeds, a continuous measurement is made of the distance of the lithium-drifted region from the opposite face of the wafer. When the drifted region reaches 30 mil or less from the back of the wafer a meter indicates the thickness of the undrifted region and, when this thickness falls below a preselected value, the temperature of the detector is automatically reduced to room temperature. The need for constant supervision of the drifting operation is thereby eliminated, and reliance on theoretical drift-rate calculations to predict the drift-through time is avoided. The technique has been applied to the manufacture of lithium -drifted silicon detectors with excellent results. The application of the technique to lithiumdrifted germanium ? detectors is also discussed briefly.

The axial and radial dependence of the netconcentrations of donors and acceptors in high-purity germanium has been investigated. The methods include dc-conductivity measurements on Czochralski grown crystals, Hall effect experiments on full area slices, collimated alpha particle probing on detectors, and C-V measurements on detector arrays. Some quantitative correlations between the results of the different methods are presented. Many of the crystals exhibit internal junctions, whose influence on the properties of high-purity germanium detectors will be discussed.

It is shown that high-purity germanium can be grown with rather simple precautions against airborne contamination. Several crystals have been grown with net impurity concentrations less than 5×10 10 /cm 3 over more than half the crystal length. Some initial results with detectors made from this materials are presented.

A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, Be(+), has a hole binding energy of about 5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The Be(+) center thermally ionizes above 4 K. It disappears at a uniaxial stress higher than about a billion dyn/sq cm parallel to (111) as a result of the lifting of the valence-band degeneracy.

Germanium detectors with reverse polarity coaxial electrodes have been shown to exhibit improved resistance to radiation damage as compared with conventional electrode devices. However, the production of reverse electrode devices involves the development of new handling and fabrication techniques which has limited their wider application. We have developed novel techniques which lead to a device which is simple to fabricate, environmentally passivated and surface state adjusted. 1) n+ Contact. The n+ contact in the central hole in the crystal is formed by lithium, electroplated from a LiNO3-KNO3 eutectic molten salt bath held at the diffusion temperature. The outside surface of the crystal is protected during electrolysis by teflon pipe tape. Electrolysis has proven to be fast and convenient and it provides a rugged surface for handling during further processing. 2) p+ Contact. The p+ contact on the outer surface of the crystal is formed by boron ion implantation. The crystal is held by a shaft through the central hole and implanted with 1015cm-2, 25 KeV boron ions. No post-implant anneal is needed. 3) Passivation and Surface State Adjustment. The open ends of the coaxial detector have their surfaces passivated and the surface states adjusted to flatband condition by sputtering germanium in an argonhydrogen mixture. A special sputtering fixture is described for conveniently mounting the detector during sputtering. Due to the combination of thin external contacts and interelectrode surface state adjustment, the detector has complete charge collection over nearly 100% of the original crystal volume.

Results demonstrating the successful use of a gold surface-barrier as a thin-window p + termination of the intrinsic region of a lithium-drifted germanium detector are reviewed; these results are a rebutal to statements recently made by Dearnaley et al. in this journal.

Multi-electrode germanium detectors are being used as an active target for decay path measurements of charmed mesons. The procedure used to fabricate such detectors is described and a brief analysis of their performance is given.

Describes the germanium monlithic detector and discusses its performance. The detector is a parallelepiped 5 x 5 x 20 mm in volume with 48 electrodes 20 mm long, 50 microns wide and spaced 50 microns one from the other deposited on one face. Presents a sketch of the detector and its working principle. To obtain a finer granularity, a telescope of 40 layers of silica was substituted with a target made out of a single block of germanium followed by a silicon telescope.

Fourier Transform Spectroscopy in the wave number range between 0 and 125/cm1 (0 to 15 meV) was used to determine the impurities producing shallow energy levels in high-purity germanium. The sensitivity of the method is sufficient to detect impurities at a concentration of 109/cm3 with excellent signal to noise ratio and the selectivity (energy resolution) allows a clean separation of all shallow levels. So far only net-concentrations can be observed so that it was necessary to measure n- and p-type material separately. The elements boron, gallium and indium appear to follow the expected segregation laws, while aluminum seems to be homogeneously distributed in the whole crystal. It has proven difficult to investigate n-type material due to the inability to produce low-noise electron-injecting contacts at the measuring temperatures (6 to 11°K).