R. L. Harper

Arsenic‐doped CdTe epilayers grown by photoassisted molecular beam epitaxy

We report the successful p‐type doping of CdTe films with arsenic using the photoassisted molecular beam epitaxy growth technique. These doped epilayers were grown at substrate temperatures as low as 180 °C. The room‐temperature hole concentrations in the CdTe:As layers ranged from 7×1015 to 6.2×1018 cm−3 as determined by van der Pauw–Hall effect measurements. We propose a doping mechanism responsible for the high p‐type doping levels observed in the films. The arsenic acceptor ionization energy was found to ∼58–60 meV using low‐temperature photoluminescence measurements.

CdTe metal‐semiconductor field‐effect transistors

We report the first demonstration of CdTe metal‐semiconductor field‐effect transistors. These transistors were fabricated using n‐type CdTe films grown by photoassisted molecular beam epitaxy. Using this new film deposition technique, it is possible to obtain highly activated n‐type or p‐type films suitable for device applications. In the present work, transistor structures with 5 or 100 μm gate lengths having channel dopings in the range from 2×1016 to 2×1017 cm−3 were fabricated and tested. The 5 μm gate devices have transconductances as large as 10 mS/mm and pinch‐off voltages of 4.0 V.

p‐type modulation‐doped HgCdTe

At North Carolina State University, we have recently employed photoassisted molecular beam epitaxy to successfully prepare p‐type modulation‐doped HgCdTe. The modulation‐doped HgCdTe samples were grown on lattice‐matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this letter, we report details of the growth experiments and describe the structural, optical, and electrical properties that this new infrared quantum alloy of HgCdTe possesses.

Properties of substitutionally doped Cd1−xMnxTe films and Cd1−xMnxTe–CdTe quantum well structures

The successful substitutional doping of thin films of the diluted magnetic semiconductor Cd1−xMnxTe is discussed. These doped films were prepared using a new technique, photoassisted molecular‐beam epitaxy, in which the substrate is illuminated during film growth. In and Sb were used as n‐ and p‐type dopants, respectively. Cd1−xMnxTe:In–CdTe and Cd1−xMnxTe:Sb–SdTe superlattices were also prepared. The structural, electrical, and optical properties of the samples were studied by means of double‐crystal x‐ray diffraction, van der Pauw Hall‐effect measurements, low‐temperature photoluminescence, and piezoreflectance measurements.

Photoluminescence spectroscopy of CdTe grown by photoassisted MBE

Abstract A study has been made of the photoluminescence (PL) properties of p-type CdTe: As and undoped n-type CdTe grown by the photoassisted molecular beam epitaxy (MBE) technique. PL studies have been performed over the temperature range from 1.6 to 300 K. Acceptor and donor ionization energies are determined from temperature dependence studies of (D 0 , h) and (e, A 0 ) PL emissions. We find that the n-type behavior in the unintentionally doped films arises from two different donor levels, and is dependent on power density during film growth. In addition, the photoassisted MBE technique has allowed a lowering of substrate growth temperatures for both CdTe:As and undoped CdTe. High quality films with bright, sharp excitonic peaks can be grown at substrate temperatures as low as 125°C.

Excited confined quantum states in CdMnTe-CdTe superlattices

The piezomodulated reflectivity spectra of CdMnTe‐CdTe superlattices grown by photoassisted molecular‐beam epitaxy reveal signatures associated with excited confined quantum states. The energies of these signatures are in excellent agreement with the predicted energies for heavy‐hole and light‐hole states calculated using a Kronig–Penney model in which strain effects are included. For comparison, we present calculations for the cases of a zero valence‐band offset and a small valence‐band offset which scales with Mn concentration.

Properties of doped CdTe films grown by photoassisted molecular‐beam epitaxy

Photoassisted molecular‐beam epitaxy (PAMBE) has been employed to grow a series of undoped and doped CdTe films. In and Sb were used as n‐type and p‐type dopants, respectively. The PAMBE‐grown epilayers exhibit outstanding electrical, optical, and structural properties as determined by van der Pauw Hall‐effect, low‐temperature photoluminescence, and double‐crystal x‐ray rocking curve measurements, respectively.

Diluted magnetic semiconductor (Cd1−xMnxTe) Schottky diodes and field‐effect transistors

We report the first demonstration of electronic devices, Schottky diodes, and metal‐semiconductor field‐effect transistors, in a diluted magnetic semiconductor Cd1−xMnxTe. These devices were fabricated using n‐type, indium‐doped CdMnTe films grown by photoassisted molecular beam epitaxy on (100) CdTe and CdZnTe substrates. Epitaxial layers with carrier concentrations of 1×1017 cm−3 and electron mobilities as large as 720 cm2/V s at 120 K were used. The Schottky diodes have turn‐on voltages of 0.8 V, idealities in the range between 1.27 and 1.7, and reverse breakdown voltages from 5.5 to 10.5 V reverse bias. The 100 μm gate length transistors have transconductances of 1 mS/mm.

Modulation‐doped HgCdTe

At North Carolina State University, we have recently employed photoassisted molecular‐beam epitaxy (MBE) to successfully prepare p‐ and n‐type modulation‐doped HgCdTe. The modulation‐doped HgCdTe samples were grown on lattice‐matched (100) CdZnTe substrates cut from boules grown at Santa Barbara Research Center. In this paper, we report details of the MBE growth experiments and describe the structural, optical, and electrical properties that this new infrared quantum alloy of HgCdTe possesses.

Properties of doped II–VI films and superlattices grown by photoassisted molecular beam epitaxy

Abstract A new film growth technique, photoassisted molecular beam epitaxy (PAMBE), has been used to prepare substitutionally doped II–VI semiconductor compounds. This epitaxial growth technique differs from conventional MBE in that the substrate is illuminated during the entire film growth process. We have used this new technique to prepare conducting layers of CdTe and CdMnTe. In our experiments, the output from an argon ion laser is used as the source of illumination. In and Sb were employed as n-type and p-type dopants, respectively. Conducting n-type CdMnTe: In-CdTe superlattices have also been grown along with doped CdMnTe: Sb-CdTe structures. The structural, electrical, and optical properties of the conducting epilayers were investigated by means of double crystal X-ray diffraction, Van der Pauw Hall effect measurements, and low temperature photoluminescence.