Impact of dopant-induced band tails on optical spectra, charge carrier transport, and dynamics in single-crystal CdTe.

Cadmium telluride (CdTe) semiconductors are used in thin-film photovoltaics, detectors, and other optoelectronic applications. For all technologies, higher efficiency and sensitivity are achieved with reduced charge carrier recombination. In this study, we use state-of-the-art CdTe single crystals and electro-optical measurements to develop a detailed understanding of recombination rate dependence on excitation and temperature in CdTe. We study recombination and carrier dynamics in high-resistivity (undoped) and arsenic (As)-doped CdTe by employing absorption, the Hall effect, time-resolved photoluminescence, and pump-probe in the 80-600 K temperature range. We report extraordinarily long lifetimes (30 µs) at low temperatures in bulk undoped CdTe. Temperature dependencies of carrier density and mobility reveal ionization of the main acceptors and donors as well as dominant scattering by ionized impurities. We also distinguish different recombination defects. In particular, shallow AsTe and deep VCd-AsCd acceptors were responsible for p-type conductivity. AX donors were responsible for electron capture, while nonradiative recombination centers (VCd-AsTe, As2 precipitates), and native defects (VCd-TeCd) were found to be dominant in p-type and n-type CdTe, respectively. Bimolecular and surface recombination rate temperature dependencies were also revealed, with bimolecular coefficient T-3/2 temperature dependence and 170 meV effective surface barrier, leading to an increase in surface recombination velocity at high temperatures and excitations. The results of this study allowed us to conclude that enhanced crucible rotation growth of As-doped CdTe is advantageous to As activation, leading to longer lifetimes and larger mobilities and open-circuit voltages due to lower absorption and trapping.

Clinico-Radiological Profile and Outcome of Airway Foreign Body Aspiration in Children: A Single-Center Experience From a Tertiary Care Center in Eastern India.

Background Foreign body aspiration is one of the leading causes of childhood morbidity and mortality among older infants and toddler age groups. Missed and delayed diagnosis of foreign body aspiration can lead to increased incidence of complications. Early diagnosis can prevent life-threatening complications and morbidity. In this study, we aimed to evaluate the clinical and radiological details, types, localization of foreign bodies, complications, and outcomes in pediatric patients who presented to our hospital with foreign body aspiration. Methodology We conducted a retrospective analysis of hospital case records of children aged one month to 14 years who were admitted to the Department of Pediatrics between June 2018 and May 2020, with clinical suspicion of foreign body aspiration. Results A total of 22 children with a diagnosis of airway foreign body were included. The mean age of presentation was three years (SD: ±2.22), with a boy-to-girl ratio of 3.4:1. Cough (81.8%) and tachypnea (72.7%) were the most common clinical symptoms. The median duration between symptom onset and diagnosis was three (interquartile range: 6) days. Unilateral reduced breath sound (81.8%) was the most common clinical examination finding. The common site of impaction was the right main bronchus in 59.1% of cases. The foreign bodies retrieved during bronchoscopy were organic substances in 63.6% of cases, with peanuts being the most common (31.8%). Chest radiographs were normal in 36.3% of cases, and common abnormalities included hyperinflation, collapse, consolidation, and mediastinal shift. Mechanical ventilation was required in 54.5% of cases. The mean duration of hospitalization was five (SD: ±2.84) days. Complications such as pneumothorax were seen in one (4.5%) case. Mortality was seen in 4.54% of cases during the bronchoscopic procedures. Conclusions Foreign body aspiration was common in young male children, with cough being the common symptom. Normal X-rays of the chest were seen in one-third of cases. The common site of impaction was the right main bronchus, and organic substances such as peanuts were common foreign bodies retrieved. Strong clinical suspicion of foreign body aspiration should be kept in cases with acute onset of cough in young children. Prompt medical attention is needed to reduce the morbidity and mortality associated with foreign body aspiration.

GLUT-1 Expression: An Aid in Complementing the WHO Oral Epithelial Dysplasia Grading System.

AIM AND OBJECTIVES: The clinicopathologic parameters alone are not sufficient to precisely predict if oral potentially malignant disorders (OPMDs) remain unchanged, i.e., without any malignant changes, regress, or advance to oral squamous cell carcinomas (OSCC). Few of the OPMDs, with or without epithelial dysplasia, may transform to frank OSCC. Discovering various molecular markers that can predict OSCC transformation is essential to develop effective therapeutic strategies. GLUT-1 is one of the hypoxia as well as metabolic indicator markers that have been used to study the metabolic activity of the cells. Hence, given by the World Health Organization (WHO), GLUT-1 expression was studied in various grades of dysplasia to see whether it complements the WHO grading system (mild, moderate, and severe). MATERIALS AND METHODS: The study was carried out on paraffin-embedded tissues of 10 normal oral mucosa and 30 OPMD cases. OPMD cases were classified into hyperkeratosis, mild dysplasia, moderate dysplasia, and severe dysplasia groups. Immunohistochemistry was carried out to evaluate the expression of GLUT-1 antigen. RESULTS: According to the WHO grading system of dysplasia, 11 (36.66%) cases were classified as hyperkeratosis, 9 (30%) cases were classified as mild dysplasia, 6 (20%) cases as moderate dysplasia, and 4 (13.33%) cases as severe dysplasia. There was a significant increase in GLUT-1 expression from normal to mild, moderate, and severe dysplasia (p value = 0.00). CONCLUSION: The expression of GLUT-1 marker complements the WHO grading system of oral epithelial dysplasia. CLINICAL SIGNIFICANCE: GLUT-1 expression can be used to complement the WHO grading system to grade epithelial dysplasia.

p-type doping efficiency in CdTe: Influence of second phase formation.

Cadmium telluride (CdTe) high purity, bulk, crystal ingots doped with phosphorus were grown by the vertical Bridgman melt growth technique to understand and improve dopant solubility and activation. Large net carrier densities have been reproducibly obtained from as-grown ingots, indicating successful incorporation of dopants into the lattice. However, net carrier density values are orders of magnitude lower than the solubility of P in CdTe as reported in literature, 1018/cm3 to 1019/cm3 [J. H. Greenberg, J. Cryst. Growth 161, 1-11 (1996) and R. B. Hall and H. H. Woodbury, J. Appl. Phys. 39(12), 5361-5365 (1968)], despite comparable starting charge dopant densities. Growth conditions, such as melt stoichiometry and post growth cooling, are shown to have significant impacts on dopant solubility. This study demonstrates that a significant portion of the dopant becomes incorporated into second phase defects as compounds of cadmium and phosphorous, such as cadmium phosphide, which inhibits dopant incorporation into the lattice and limits maximum attainable net carrier density in bulk crystals. Here, we present an extensive study on the characteristics of these second phase defects in relation to their composition and formation kinetics while providing a pathway to minimize their formation and enhance solubility.

Self-compensation in arsenic doping of CdTe.

Efficient p-type doping in CdTe has remained a critical challenge for decades, limiting the performance of CdTe-based semiconductor devices. Arsenic is a promising p-type dopant; however, reproducible doping with high concentration is difficult and carrier lifetime is low. We systematically studied defect structures in As-doped CdTe using high-purity single crystal wafers to investigate the mechanisms that limit p-type doping. Two As-doped CdTe with varying acceptor density and two undoped CdTe were grown in Cd-rich and Te-rich environments. The defect structures were investigated by thermoelectric-effect spectroscopy (TEES), and first-principles calculations were used for identifying and assigning the experimentally observed defects. Measurements revealed activation of As is very low in both As-doped samples with very short lifetimes indicating strong compensation and the presence of significant carrier trapping defects. Defect studies suggest two acceptors and one donor level were introduced by As doping with activation energies at ~88 meV, ~293 meV and ~377 meV. In particular, the peak shown at ~162 K in the TEES spectra is very prominent in both As-doped samples, indicating a signature of AX-center donors. The AX-centers are believed to be responsible for most of the compensation because of their low formation energy and very prominent peak intensity in TEES spectra.

An unusual presentation of extranodal Rosai-Dorfman disease threatening the airway.

Rosai-Dorfman disease (RDD) is a rare benign systemic histiocytic proliferation, characterized by massive lymph node enlargement and sometimes associated with extranodal involvement. Even though it is considered as a benign disease, fatalities can occur due to its unusually large size and its location. Our case highlighting a primary extranodal site of vallecula, which is extremely rare and not reported in literature before. It presented with almost complete obstructing the oropharyngeal airway creating a life threatening situation, needed emergency tracheostomy.

Isolated case of mucosal histoid Hansen's disease of the nasal cavity in a post-global elimination era.

Histoid Hansen's disease is a rare form of multibacillary leprosy with distinct clinical and histopathological features. This type of leprosy is a variant of lepromatous leprosy with a very high bacterial reserve. Of alarming concern is the discovery of an isolated mucosal histoid leprotic lesion inside the nasal cavity of a patient in the post-global leprosy elimination era. Our case had no history of leprosy or exposure to dapsone/multidrug therapy but had a heavy bacillary index. We are reporting this case to highlight the rarity of mucosal lesions due to histoid leprosy and involvement of the nasal cavity, as well as to create awareness and avoid misdiagnosis. This will help facilitate prompt treatment to minimize the complications and deformities of the patient and prevent its spread throughout the community.