Marshall I. Nathan

Raman spectra of glassy carbon

The Raman spectrum of glassy carbon has been measured. Two broad lines are observed at 1340 and 1590 cm−1. These results are consistent with the turbostratic structure, which has been suggested for glassy carbon, with a particle size La of approximately 30 A.

Characteristics of AuGeNi ohmic contacts to GaAs

Abstract We have studied AuGeNi ohmic contacts to n-type MBE grown GaAs epitaxial-layer with doping in the (1016−1019) cm−3 range, and found several new effects: (a) Contact resistivity exhibit a weak dependence on carrier concentration (much weaker than 1/ND depencence); (b) We find evidence for a high resistivity layer under the contact at least several thousands angstroms deep, which dominate the contact resistance in most cases; (c) We find a peripheral zone around the contact, about 1 μm wide which differs chemically from the GaAs epi-layer; (d) SIMS analysis reveals a deep diffusion into the GaAs of Ni and Ge; (e) Correlation between density of GeNi clusters in the contact and the contact resistivity are found; (f) Temperature measurements justify that tunneling is responsible for the ohmic contact. We discuss also the validity of the transmission line method and the commonly accepted model of the contact.

Tunneling hot-electron transfer amplifier: a hot-electron GaAs device with current gain

Tunneling hot‐electron transfer amplifier (THETA) devices, based on GaAs‐AlGaAs heterojunctions, were fabricated and tested. Hot‐electron transfer (α) through a 1100‐A base in excess of 70% was found at 4.2 K. This resulted in a corresponding current gain ( β) in a common emitter configuration of about 2.3. In the temperature range of 4.2–80 K and under constant biasing conditions, α was nearly temperature independent. Electron energy distributions for motion normal to the layers and electron total energy loss while traversing the device were estimated. Typical widths of the energy distributions were less than 200 meV, and both widths and energy peak positions were only slightly dependent on temperature and initial injection energy.

GaAs Injection Laser with Novel Mode Control and Switching Properties

The effects of nonuniform current densities on the properties of GaAs injection lasers are investigated. The structure studied is an injection laser with a channel etched on the p side of the junction parallel to the reflecting ends. It is found that the threshold current is higher for nonuniform currents than for uniform currents. The mode in which the laser oscillates depends on the distribution of current. A simple model of the transition and the energy vs density of states for the semiconductor is presented to explain these effects. Bistable operation of the structure has been observed.

Electron mobility in p‐type GaAs

The mobility of electrons in p‐type GaAs, μPn has been determined by measuring the common emitter cutoff frequency fT of heterojunction bipolar transistors with a wide, uniformly doped base. At 295 K, μPn =1150 cm2/(V s) is found for a hole concentration of 3.6×1018 cm−3. At 77 K, μPn =6000 cm2/(V s). The room‐temperature value is considerably smaller and the 77 K value considerably larger than the electron mobility in comparably doped n‐type material.

Persistent photoconductivity in AlGaAs/GaAs modulation doped layers and field effect transistors: A review

Abstract The phenomenon of persistent photoconductivity in AlGaAs/GaAs modulation-doped layers and transistors is reviewed. Experimental observations, mechanisms which are responsible for it and structures for its elimination are discussed.

Energy band discontinuities in heterojunctions measured by internal photoemission

A novel method involving internal photoemission has been developed to determine the conduction band discontinuity Δ Ec of heterojunctions. The method is straightforward, accurate, and assumes minimum unknowns; and has been applied to GaAs/AlxGa1−xAs heterojunctions. We have found for x 0.4, the apparent Δ Ec is considerably smaller.

GUNN EFFECT IN n‐TYPE InSb

In this letter we report the observation of the Gunn effect in n‐type InSb at 77°K and atmospheric pressure. This result is surprising, since it was previously thought that the large amount of carrier multiplication at fields below the Gunn threshold would preclude observation of the Gunn effect in InSb and similar materials. Several explanations for the negative differential conductivity underlying the Gunn effect in this case are possible, but the intervalley transfer mechanism is most consistent with the observed negative pressure coefficient of the threshold field.

Barrier heights and electrical properties of intimate metal‐AlGaAs junctions

The dependence of the Schottky barrier height of Mo‐n:AlGaAs junctions, fabricated in situ by molecular beam epitaxy, on the Al mole fraction (x) was determined by internal photoemission measurements and by activation energy plots of the current versus voltage dependence on temperature. Both techniques yielded similar values. The difference in barrier height of Mo‐AlGaAs as a function of x, compared to that of Mo‐GaAs, was found to be equal to the conduction band discontinuity in AlGaAs‐GaAs heterojunctions for Al concentrations in the range 0≤x≤0.4. For x>0.4, values of the barrier heights were somewhat lower than values of the band discontinuity; however, both dependencies on x were quite similar. The temperature dependence of the current‐voltage characteristics showed that thermionic emission was the dominant transport mechanism at forward bias for temperatures higher than 250 K. At lower temperatures, current transport was governed by thermionic field emission.

Light Emission from Reverse Biased GaAs and InP p‐n Junctions

The light emission from reverse‐biased diffused p‐n junctions made in the direct band gap semiconductors GaAs and InP has been measured. In addition to the broad emission spectrum observed from junctions in other materials which have indirect band gaps, a sharp line (Δλ≅150 A) is observed at photon energies slightly less than the energy gap. In most diodes this line dominates the spectrum. It is almost identical in shape to the line observed at this photon energy when the junction is forward biased. The measured external quantum efficiency of the reverse biased light is higher (∼10−5 to 10−4) than has been reported for most other materials. The spatial distribution of the light emission and the current‐voltage characteristics have also been found to be similar to those of other materials.